Changelog for golds-gym-0.3.0.0

Changelog

Lens-based expectation combinators for custom performance assertions
- New Test.Hspec.BenchGolden.Lenses module with van Laarhoven lenses for GoldenStats fields
- Lenses: _statsMean, _statsMedian, _statsTrimmedMean, _statsStddev, _statsMAD, _statsIQR, _statsMin, _statsMax
- Smart metric selectors: metricFor and varianceFor automatically choose appropriate lens based on BenchConfig
- Expectation type for composable performance assertions
- Tolerance variants: Percent, Absolute, Hybrid, MustImprove, MustRegress
- Boolean composition operators: (&&~) for AND, (||~) for OR
- Infix operators: (@~) for percentage, (@<) for absolute, (@<<) for must-improve, (@>>) for must-regress
- benchGoldenWithExpectation combinator for custom lens-based expectations
- Enables assertions like "must be 10% faster", "median within 10%", "IQR < 0.1ms"
Tolerance helper functions for manual comparison
- withinPercent, withinAbsolute, withinHybrid for tolerance checking
- mustImprove, mustRegress for directional performance expectations
- percentDiff, absDiff utilities

Refactored comparison logic to use lenses internally (non-breaking)
- compareStats now uses metricFor instead of if/else branching
- checkVariance now uses varianceFor for cleaner metric selection

Hybrid tolerance mechanism to prevent false failures from measurement noise
- New absoluteToleranceMs field in BenchConfig (default: Just 0.01 ms)
- Benchmarks now pass if EITHER percentage tolerance OR absolute tolerance is satisfied
- Eliminates random failures for sub-millisecond operations where measurement noise causes large percentage variations despite negligible absolute differences
Enhanced failure messages showing both tolerance thresholds
- Regression/improvement messages now display: "tolerance: 15.0% or 0.010 ms" when absolute tolerance is configured
Example benchmarks demonstrating tolerance configurations
- Hybrid tolerance (default)
- Percentage-only tolerance
- Strict absolute tolerance
- Relaxed tolerance for CI environments

Default BenchConfig now includes absoluteToleranceMs = Just 0.01 (10 microseconds)
BenchResult constructors (Regression, Improvement) now include Maybe Double for absolute tolerance
Updated "sort already sorted" example to use robust statistics to handle outliers
Increased tolerance for percentage-only example to 30% to reduce false failures

Random benchmark failures for fast operations (< 1ms) due to measurement noise
False regressions when absolute time differences are negligible but percentage variations are large
Inconsistent test results across runs for sub-millisecond operations