feat: add color string format rules

[nieomylnieja]

Motivation

pkg/rules was missing common color string format validators that users otherwise had to reimplement in application code.

Summary

Added color string format rules with exported error codes, message templates, validation-plan descriptions, and focused tests.

Testing

Added rule tests covering accepted examples, invalid messages, and error-code assertions.

Release Notes

Added rules.StringHexColor, rules.StringRGB, rules.StringRGBA, rules.StringHSL, rules.StringHSLA, and rules.StringCMYK.

[github-actions]

Test coverage changes:

Package	Before	After	Diff
github.com/nobl9/govy/cmd/govy	0%	0%	✔️
github.com/nobl9/govy/internal	73%	73%	✔️
github.com/nobl9/govy/internal/collections	100%	100%	✔️
github.com/nobl9/govy/internal/inferpath	76%	76%	✔️
github.com/nobl9/govy/internal/messagetemplates	89%	89%	✔️
github.com/nobl9/govy/internal/stringconvert	86%	86%	✔️
github.com/nobl9/govy/internal/typeinfo	94%	94%	✔️
github.com/nobl9/govy/pkg/govy	93%	93%	✔️
github.com/nobl9/govy/pkg/govytest	100%	100%	✔️
github.com/nobl9/govy/pkg/jsonpath	85%	85%	✔️
github.com/nobl9/govy/pkg/rules	98%	98%	✔️

[n9-machine-user]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'Govy Go Benchmark'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.50.

Benchmark suite	Current: 0a3eca4	Previous: ab7dfb6	Ratio
BenchmarkStringRGB (github.com/nobl9/govy/pkg/rules)	71380 ns/op 84.00 validations/op 43077 B/op 694 allocs/op	9545 ns/op 8096 B/op 132 allocs/op	7.48
BenchmarkStringRGB (github.com/nobl9/govy/pkg/rules) - ns/op	71380 ns/op	9545 ns/op	7.48
BenchmarkStringRGB (github.com/nobl9/govy/pkg/rules) - B/op	43077 B/op	8096 B/op	5.32
BenchmarkStringRGB (github.com/nobl9/govy/pkg/rules) - allocs/op	694 allocs/op	132 allocs/op	5.26
BenchmarkStringHSL (github.com/nobl9/govy/pkg/rules)	50296 ns/op 68.00 validations/op 28992 B/op 470 allocs/op	7919 ns/op 6672 B/op 108 allocs/op	6.35
BenchmarkStringHSL (github.com/nobl9/govy/pkg/rules) - ns/op	50296 ns/op	7919 ns/op	6.35
BenchmarkStringHSL (github.com/nobl9/govy/pkg/rules) - B/op	28992 B/op	6672 B/op	4.35
BenchmarkStringHSL (github.com/nobl9/govy/pkg/rules) - allocs/op	470 allocs/op	108 allocs/op	4.35
BenchmarkStringFileSystemPath (github.com/nobl9/govy/pkg/rules)	45467 ns/op 9913 B/op 117 allocs/op	22627 ns/op 9801 B/op 117 allocs/op	2.01
BenchmarkStringFileSystemPath (github.com/nobl9/govy/pkg/rules) - ns/op	45467 ns/op	22627 ns/op	2.01
BenchmarkStringFilePath (github.com/nobl9/govy/pkg/rules)	46366 ns/op 10458 B/op 129 allocs/op	23333 ns/op 10457 B/op 129 allocs/op	1.99
BenchmarkStringFilePath (github.com/nobl9/govy/pkg/rules) - ns/op	46366 ns/op	23333 ns/op	1.99
BenchmarkStringDirPath (github.com/nobl9/govy/pkg/rules)	45534 ns/op 10169 B/op 124 allocs/op	23277 ns/op 10169 B/op 124 allocs/op	1.96
BenchmarkStringDirPath (github.com/nobl9/govy/pkg/rules) - ns/op	45534 ns/op	23277 ns/op	1.96

This comment was automatically generated by workflow using github-action-benchmark.

CC: @nieomylnieja