Revert "Mimalloc v3 update (oven-sh#26379)" (oven-sh#26783)

This reverts commit c63415c.

### What does this PR do?

### How did you verify your code works?

Update WebKit (oven-sh#26549)

### What does this PR do?

Includes
oven-sh/WebKit@9a2cc42

Fixes #oven-sh#26525

### How did you verify your code works?

CI

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Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>

fix(shell): handle ".", "", "./" in cwd() by using process.cwd() (ove…

…n-sh#26461)

## Summary
- Fix `$`...`.cwd(".")` causing ENOENT error with path ending in
"undefined"
- The same fix applies to `.cwd("")` and `.cwd("./")`
- Falls back to `process.cwd()` when `defaultCwd` is undefined

Closes oven-sh#26460

## Test plan
- [x] Added regression test in `test/regression/issue/26460.test.ts`
- [x] Verified test fails with `USE_SYSTEM_BUN=1` (reproduces the bug)
- [x] Verified test passes with `bun bd test` (fix works)

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Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

fix(css): restore handler context after minifying nested rules (oven-…

…sh#25997)

## Summary
- Fixes handler context not being restored after minifying nested CSS
rules
- Adds regression test for the issue

## Test plan
- [x] Test fails with `USE_SYSTEM_BUN=1 bun test
test/regression/issue/25794.test.ts`
- [x] Test passes with `bun bd test test/regression/issue/25794.test.ts`

Fixes oven-sh#25794

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Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

fix: v8::Value::IsInt32()/IsUint32() edge cases (oven-sh#25548)

### What does this PR do?

- fixes both functions returning false for double-encoded values (even
if the numeric value is a valid int32/uint32)
- fixes IsUint32() returning false for values that don't fit in int32
- fixes the test from oven-sh#22462 not testing anything (the native functions
were being passed a callback to run garbage collection as the first
argument, so it was only ever testing what the type check APIs returned
for that function)
- extends the test to cover the first edge case above

### How did you verify your code works?

The new tests fail without these fixes.

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Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

fix(compile): use 8-byte header for embedded section to ensure byteco…

…de alignment (oven-sh#25377)

## Summary
- Change the size header in embedded Mach-O and PE sections from `u32`
(4 bytes) to `u64` (8 bytes)
- Ensures the data payload starts at an 8-byte aligned offset, which is
required for the bytecode cache

## Test plan
- [x] Test standalone compilation on macOS
- [ ] Test standalone compilation on Windows

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test(ENG-21524): Fuzzilli Stop-Gap (oven-sh#24826)

### What does this PR do?

Adds [@mschwarzl's Fuzzilli Support
PR](oven-sh#23862) with the changes
necessary to be able to:

- Run it in CI
- Make no impact on `debug` and `release` mode.

### How did you verify your code works?

---------

Co-authored-by: Martin Schwarzl <mschwarzl@cloudflare.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Dylan Conway <dylan.conway567@gmail.com>

ci: run modified tests first (oven-sh#24463)

Co-authored-by: Meghan Denny <meghan@bun.com>

Refactor napi_env to use Ref-counted NapiEnv (oven-sh#23940)

### What does this PR do?

Replaces raw napi_env pointers with WTF::Ref<NapiEnv> for improved
memory management and safety. Updates related classes, function
signatures, and finalizer handling to use reference counting. Adds
ref/deref methods to NapiEnv and integrates them in Zig and C++ code
paths, ensuring proper lifecycle management for N-API environments.

### How did you verify your code works?

Update no-validate-leaksan.txt