…lkey-io#3174)

I was working on ASAN large memory tests when I countered this issue.

The issue was that the hardcoded `999` key could land in an early
bucket. Then shrink rehash could finish early, and later inserts could
trigger a new expansion rehash, resetting rehash_idx low. The test now
picks the survivor key dynamically as the key mapped to the highest
bucket index.

```
[test_hashtable.c] Memory leak detected of 336 bytes
=================================================================
==3901==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 80 byte(s) in 1 object(s) allocated from:
    #0 0x7fb0556fd9c7 in malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:69
    #1 0x563bfdf4c47d in ztrymalloc_usable_internal /home/runner/work/valkey/valkey/src/zmalloc.c:156
    #2 0x563bfdf4c47d in valkey_malloc /home/runner/work/valkey/valkey/src/zmalloc.c:185
    #3 0x563bfdd42eaf in hashtableCreate /home/runner/work/valkey/valkey/src/hashtable.c:1217
    #4 0x563bfdaa1cbf in test_empty_buckets_rehashing unit/test_hashtable.c:232
    #5 0x563bfdae772b in runTestSuite unit/test_main.c:36
    #6 0x563bfda86b20 in main unit/test_main.c:108
    #7 0x7fb05522a1c9  (/lib/x86_64-linux-gnu/libc.so.6+0x2a1c9) (BuildId: 274eec488d230825a136fa9c4d85370fed7a0a5e)
    #8 0x7fb05522a28a in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2a28a) (BuildId: 274eec488d230825a136fa9c4d85370fed7a0a5e)
    #9 0x563bfda8a5c4 in _start (/home/runner/work/valkey/valkey/src/valkey-unit-tests+0x17c5c4) (BuildId: 44cfc183e6e82e499bcc9f6adc094d7f774ee9d2)

Indirect leak of 128 byte(s) in 1 object(s) allocated from:
    #0 0x7fb0556fd340 in calloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:77
    #1 0x563bfdf4c922 in ztrycalloc_usable_internal /home/runner/work/valkey/valkey/src/zmalloc.c:214
    #2 0x563bfdf4c922 in valkey_calloc /home/runner/work/valkey/valkey/src/zmalloc.c:257
    #3 0x563bfdd40967 in resize /home/runner/work/valkey/valkey/src/hashtable.c:741
    #4 0x563bfdd45eb1 in hashtableExpandIfNeeded /home/runner/work/valkey/valkey/src/hashtable.c:1446
    #5 0x563bfdd45eb1 in hashtableExpandIfNeeded /home/runner/work/valkey/valkey/src/hashtable.c:1433
    #6 0x563bfdd45eb1 in insert /home/runner/work/valkey/valkey/src/hashtable.c:1041
    #7 0x563bfdd45eb1 in hashtableAddOrFind /home/runner/work/valkey/valkey/src/hashtable.c:1554
    #8 0x563bfdd45eb1 in hashtableAdd /home/runner/work/valkey/valkey/src/hashtable.c:1539
    #9 0x563bfdaa1e3b in test_empty_buckets_rehashing unit/test_hashtable.c:254
    #10 0x563bfdae772b in runTestSuite unit/test_main.c:36
    #11 0x563bfda86b20 in main unit/test_main.c:108
    #12 0x7fb05522a1c9  (/lib/x86_64-linux-gnu/libc.so.6+0x2a1c9) (BuildId: 274eec488d230825a136fa9c4d85370fed7a0a5e)
    #13 0x7fb05522a28a in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2a28a) (BuildId: 274eec488d230825a136fa9c4d85370fed7a0a5e)
    #14 0x563bfda8a5c4 in _start (/home/runner/work/valkey/valkey/src/valkey-unit-tests+0x17c5c4) (BuildId: 44cfc183e6e82e499bcc9f6adc094d7f774ee9d2)

Indirect leak of 64 byte(s) in 1 object(s) allocated from:
    #0 0x7fb0556fd340 in calloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:77
    #1 0x563bfdf4c922 in ztrycalloc_usable_internal /home/runner/work/valkey/valkey/src/zmalloc.c:214
    #2 0x563bfdf4c922 in valkey_calloc /home/runner/work/valkey/valkey/src/zmalloc.c:257
    #3 0x563bfdd3f553 in bucketConvertToChained /home/runner/work/valkey/valkey/src/hashtable.c:908
    #4 0x563bfdd3f553 in findBucketForInsert /home/runner/work/valkey/valkey/src/hashtable.c:1021
    #5 0x563bfdd45d9e in insert /home/runner/work/valkey/valkey/src/hashtable.c:1045
    #6 0x563bfdd45d9e in hashtableAddOrFind /home/runner/work/valkey/valkey/src/hashtable.c:1554
    #7 0x563bfdd45d9e in hashtableAdd /home/runner/work/valkey/valkey/src/hashtable.c:1539
    #8 0x563bfdaa1e3b in test_empty_buckets_rehashing unit/test_hashtable.c:254
    #9 0x563bfdae772b in runTestSuite unit/test_main.c:36
    #10 0x563bfda86b20 in main unit/test_main.c:108
    #11 0x7fb05522a1c9  (/lib/x86_64-linux-gnu/libc.so.6+0x2a1c9) (BuildId: 274eec488d230825a136fa9c4d85370fed7a0a5e)
    #12 0x7fb05522a28a in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2a28a) (BuildId: 274eec488d230825a136fa9c4d85370fed7a0a5e)
    #13 0x563bfda8a5c4 in _start (/home/runner/work/valkey/valkey/src/valkey-unit-tests+0x17c5c4) (BuildId: 44cfc183e6e82e499bcc9f6adc094d7f774ee9d2)

Indirect leak of 64 byte(s) in 1 object(s) allocated from:
    #0 0x7fb0556fd340 in calloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:77
    #1 0x563bfdf4c922 in ztrycalloc_usable_internal /home/runner/work/valkey/valkey/src/zmalloc.c:214
    #2 0x563bfdf4c922 in valkey_calloc /home/runner/work/valkey/valkey/src/zmalloc.c:257
    #3 0x563bfdd40967 in resize /home/runner/work/valkey/valkey/src/hashtable.c:741
    #4 0x563bfdaa1df8 in test_empty_buckets_rehashing unit/test_hashtable.c:248
    #5 0x563bfdae772b in runTestSuite unit/test_main.c:36
    #6 0x563bfda86b20 in main unit/test_main.c:108
    #7 0x7fb05522a1c9  (/lib/x86_64-linux-gnu/libc.so.6+0x2a1c9) (BuildId: 274eec488d230825a136fa9c4d85370fed7a0a5e)
    #8 0x7fb05522a28a in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2a28a) (BuildId: 274eec488d230825a136fa9c4d85370fed7a0a5e)
    #9 0x563bfda8a5c4 in _start (/home/runner/work/valkey/valkey/src/valkey-unit-tests+0x17c5c4) (BuildId: 44cfc183e6e82e499bcc9f6adc094d7f774ee9d2)

SUMMARY: AddressSanitizer: 336 byte(s) leaked in 4 allocation(s).
```

Signed-off-by: Sarthak Aggarwal <sarthagg@amazon.com>

CI caught ip and name SDS allocations being leaked in
fetchClusterConfiguration. The ip SDS was copied again via sdsnew()
before being passed to createClusterNode(), leaking the original. The
name SDS was leaked when the node already existed in the dict.

Free ip and name on all exit paths in fetchClusterConfiguration. Remove
stale guard in freeClusterNode, no longer needed since valkey-io#1392

CI Error -
```
Direct leak of 33 byte(s) in 3 object(s) allocated from:
      #0 0x7f4c3a0fd9c7 in malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:69
      #1 0x5564620c124a in ztrymalloc_usable_internal /home/runner/work/valkey/valkey/src/zmalloc.c:172
      #2 0x5564620c124a in zmalloc_usable /home/runner/work/valkey/valkey/src/zmalloc.c:268
      #3 0x5564620dfbe6 in _sdsnewlen.constprop.0 /home/runner/work/valkey/valkey/src/sds.c:102
      #4 0x556462050996 in sdsnewlen /home/runner/work/valkey/valkey/src/sds.c:169
      #5 0x556462050996 in sdsnew /home/runner/work/valkey/valkey/src/sds.c:185
      #6 0x556462050996 in fetchClusterConfiguration /home/runner/work/valkey/valkey/src/valkey-benchmark.c:1477
```

Issue was reproduceable locally using `leaks --atExit`

Signed-off-by: nmvk <r@nmvk.com>