v4.1.0

Bug-fix release: 24 bugs fixed across the circuit state machine, rolling
metrics, and configuration factories. No breaking API changes (verified
with gorelease). Requires Go 1.21+.

- SortedDurations.Percentile(NaN) panicked with index-out-of-range (#152)
- RollingCounter.GetBuckets panicked on zero-value counter (divide by zero) (#151)
- RollingCounter.UnmarshalJSON panicked on incomplete JSON; now errors (#151)
- RollingCounter.UnmarshalJSON accepted inconsistent JSON (NumBuckets vs
  Buckets length mismatch), later GetBuckets panicked; now errors (#152)
- Opener.SetConfigNotThreadSafe panicked on nil Now func (#151)
- RollingBuckets.Advance panicked on zero BucketWidth (#150)
- RollingPercentile.AddDuration panicked on times before StartTime (#150)

- ConsecutiveErrOpenerFactory: closure captured config by reference,
  concurrent factory calls mutated shared state (#151)
- hystrix.OpenerFactory and CloserFactory: same closure-capture bug (#150)
- RollingBuckets.Advance: concurrent callers could clear the same bucket
  multiple times or skip clears (#150)

- Circuit open/close TOCTOU: concurrent state transitions could emit
  Opened()/Closed() metric callbacks multiple times per transition.
  Now uses CAS to guarantee exactly-once (#151)
- Fallback concurrency throttle read MaxConcurrentRequests twice; a
  config change between reads could produce inconsistent gating (#151)
- Circuit.OpenCircuit used time.Now() instead of the configured TimeKeeper (#150)
- Duplicate now() calls at timeout boundary could mark an on-time
  completion as a spurious timeout (#150)
- SortedDurations.Var reported percentiles with wrong scaling (#150)
- MockClock.AfterFunc with negative duration never fired (real
  time.AfterFunc fires immediately) (#151)
- errors.IsBadRequest did not unwrap wrapped errors (now uses errors.As) (#150)

- Removed unreachable branches and unused fields flagged by static analysis.

- Property-based state-machine test (testing/quick + MockClock + reference
  model) verifies the exactly-once RunMetrics contract and Opened/Closed
  alternation under all interleavings (#152)
- 5 Go-native fuzz targets with differential oracle for RollingCounter,
  RollingBuckets, SortedDurations.Percentile (#152)
- Invariant-asserting concurrent stress tests that would have caught the
  TOCTOU bugs pre-merge (#152)
- Daily scheduled fuzzing workflow (#152)

- Makefile restored: make (fast loop), make ci (pre-PR gate),
  make fuzz, make bench, make cover (#152)

Full changelog: v4.0.0...v4.1.0

ci: Add circuit test

Add AfterFunc configuration option to hystrix.ConfigureCloser (#111)

* Add AfterFunc configuration option to hystrix.ConfigureCloser

* Add AfterFunc field to ConfigureCloser Merge function

* Add json tag to omit AfterFunc from json encoding

Signed-off-by: Chris Guiney <chrisg@tune.com>

Co-authored-by: Chris Guiney <chrisg@tune.com>

[trivial] remove benchmark dependencies from v3 (#109)

* remove benchmark dependencies from v3

* add replace directive

Zuzmic treat deadline expired as failure (#95)

* treat DeadlineExceeded as failure

* remove comment: typo alrady fixed

* add IsErrInterrupt config option

* remove mutex

* fix ordering

* circle/circuit

Co-authored-by: Kolokhanin Roman <rkolokhanin@ozon.ru>

Add license to v3 directory (#91)

* Add license to v3 directory

I think pkg.go.dev is not detecting
the license because it is in the ROOT and not in v3
directory.  Add a copy to the v3 directory as well.

* go mod only requires 1.11

Merge pull request #78 from cep21/pr

Error: add Error type.

Merge pull request #76 from cep21/modules

modules: tidy and fix some module corner cases

Fix misspells

Upgrade to 1.12 and golangci-lint (#61)

* Upgrade to 1.12 and golangci-lint

* Unused gometalinter install script