feat: add optional caching of params and constants

[pboyd04]

If you have a bunch of govaluate expressions kept in memory with similar parameters and/or similar constants this allows you to turn on a cache with a build tag (assuming you have golang 1.24 or greater). This reduces the amount of memory the expressions consume by sharing stages across expressions.

Benchmarks without cache:

BenchmarkSingleParse-24                          4112127               289.5 ns/op           224 B/op          6 allocs/op
BenchmarkSimpleParse-24                           709797              1628 ns/op            1211 B/op         29 allocs/op
BenchmarkFullParse-24                             209383              6999 ns/op            4687 B/op        116 allocs/op
BenchmarkEvaluationSingle-24                    128901000                8.998 ns/op           0 B/op          0 allocs/op
BenchmarkEvaluationNumericLiteral-24            43751962                25.94 ns/op            0 B/op          0 allocs/op
BenchmarkEvaluationLiteralModifiers-24          17263702                71.93 ns/op            8 B/op          1 allocs/op
BenchmarkEvaluationParameter-24                 76307056                16.52 ns/op            0 B/op          0 allocs/op
BenchmarkEvaluationParameters-24                37903912                35.15 ns/op            0 B/op          0 allocs/op
BenchmarkEvaluationParametersModifiers-24       10787078                99.12 ns/op           16 B/op          2 allocs/op
BenchmarkComplexExpression-24                   71083309                17.57 ns/op            0 B/op          0 allocs/op
BenchmarkRegexExpression-24                      1591404               762.6 ns/op          1428 B/op         18 allocs/op
BenchmarkConstantRegexExpression-24              8835997               187.5 ns/op             0 B/op          0 allocs/op
BenchmarkAccessors-24                           14347064                75.44 ns/op            8 B/op          1 allocs/op
BenchmarkAccessorMethod-24                       3005412               407.0 ns/op           168 B/op          7 allocs/op
BenchmarkAccessorMethodParams-24                 2729622               464.5 ns/op           208 B/op          8 allocs/op
BenchmarkNestedAccessors-24                     11189446               100.7 ns/op             0 B/op          0 allocs/op

Benchmarks with cache:

BenchmarkSingleParse-24                          4696720               259.4 ns/op           120 B/op          4 allocs/op
BenchmarkSimpleParse-24                           744771              1548 ns/op             794 B/op         21 allocs/op
BenchmarkFullParse-24                             220964              7149 ns/op            3226 B/op         88 allocs/op
BenchmarkEvaluationSingle-24                    100000000               10.97 ns/op            0 B/op          0 allocs/op
BenchmarkEvaluationNumericLiteral-24            31738222                38.02 ns/op            0 B/op          0 allocs/op
BenchmarkEvaluationLiteralModifiers-24          13775227                85.30 ns/op            8 B/op          1 allocs/op
BenchmarkEvaluationParameter-24                 41696491                28.30 ns/op            0 B/op          0 allocs/op
BenchmarkEvaluationParameters-24                22658908                53.23 ns/op            0 B/op          0 allocs/op
BenchmarkEvaluationParametersModifiers-24       10979146               108.7 ns/op            16 B/op          2 allocs/op
BenchmarkComplexExpression-24                   52387562                22.92 ns/op            0 B/op          0 allocs/op
BenchmarkRegexExpression-24                      1585320               757.0 ns/op          1431 B/op         18 allocs/op
BenchmarkConstantRegexExpression-24              5570799               212.2 ns/op             0 B/op          0 allocs/op
BenchmarkAccessors-24                           14245064                83.62 ns/op            8 B/op          1 allocs/op
BenchmarkAccessorMethod-24                       2444245               483.7 ns/op           168 B/op          7 allocs/op
BenchmarkAccessorMethodParams-24                 2501234               485.1 ns/op           208 B/op          8 allocs/op
BenchmarkNestedAccessors-24                     10499632               114.6 ns/op             0 B/op          0 allocs/op

[Copilot]

Pull Request Overview

This PR introduces optional caching of evaluation stages for parameters and constants to reduce memory usage when multiple govaluate expressions share similar values. The caching is enabled through a build tag and requires Go 1.24+ to leverage weak pointers.

• Refactored stage planning to use cached stages for parameters and constants
• Implemented build-tag conditional caching using weak references to avoid memory leaks
• Added defensive copying to prevent mutation of shared cached stages

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
stagePlanner.go	Modified to use new caching functions and added defensive copying for shared stages
noCache.go	Fallback implementation that maintains original behavior without caching
cache.go	Cache implementation using weak pointers and sync.Map for Go 1.24+

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[Copilot]

The build constraint 'go1.24' may not work as expected. Go build tags typically use version formats like 'go1.24.0' or semantic versioning. Consider using a more standard build tag format.

Suggested change

	//go:build go1.24 && cache
	//go:build go1.24.0 && cache

[Copilot]

The build constraint '!go1.24' should match the format used in cache.go. If cache.go uses 'go1.24', this constraint should be '!go1.24', but consider using a more standard build tag format consistently.

Suggested change

	//go:build !go1.24 || !cache
	//go:build !(go1.24 && cache)

[github-actions]

🎉 This PR is included in version 1.10.0 🎉

The release is available on GitHub release

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