Add comprehensive case conversion utilities

[karngyan]

Add comprehensive case conversion utilities

This PR introduces several new string case conversion functions to complement the existing PascalCase functionality:

New Functions Added:

• CamelCase: Converts strings to camelCase format
• KebabCase: Converts strings to kebab-case with customizable separators
• SnakeCase: Converts strings to snake_case format
• TrainCase: Converts strings to Train-Case format
• FlatCase: Converts strings to flatcase (no separators)
• UpperFirst: Capitalizes first character
• LowerFirst: Lowercases first character

Key Improvements:

• Enhanced joinWords function to handle empty word filtering
• Support for generic types with StringOrStringSlice constraint
• Comprehensive test coverage for all new functions including edge cases
• Consistent API design across all case conversion functions

Testing:

• 254 new test cases covering various input scenarios
• Edge case handling for unicode characters, numbers, and mixed separators
• Full backward compatibility maintained

All functions support both string and []string inputs with type safety through generics.

[Copilot]

Pull Request Overview

This PR adds comprehensive case conversion utilities to complement the existing PascalCase functionality. The implementation provides seven new string manipulation functions that handle various common case formats.

• Adds CamelCase, KebabCase, SnakeCase, TrainCase, FlatCase, UpperFirst, and LowerFirst functions
• Enhances the joinWords function to support empty word filtering for better case conversion handling
• Provides comprehensive test coverage with 254 new test cases covering edge cases and various input scenarios

Reviewed Changes

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

File	Description
sx.go	Implements seven new case conversion functions and enhances joinWords with empty word filtering
sx_test.go	Adds comprehensive test coverage for all new case conversion functions
.cursor/commands/pr.md	Adds PR creation workflow documentation

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[github-actions]

📊 Code Coverage Report

total:					(statements)			88.7%

Coverage by file

github.com/gomantics/sx/sx.go:14:	isSeparator			100.0%
github.com/gomantics/sx/sx.go:19:	isSeparatorCustom		100.0%
github.com/gomantics/sx/sx.go:24:	isLetterCaseChange		100.0%
github.com/gomantics/sx/sx.go:51:	splitByCaseWithCustomSeparators	100.0%
github.com/gomantics/sx/sx.go:124:	defaultSplitConfig		100.0%
github.com/gomantics/sx/sx.go:131:	WithSeparators			100.0%
github.com/gomantics/sx/sx.go:140:	SplitByCase			100.0%
github.com/gomantics/sx/sx.go:150:	normalizeWord			100.0%
github.com/gomantics/sx/sx.go:158:	capitalizeWord			66.7%
github.com/gomantics/sx/sx.go:172:	joinWords			100.0%
github.com/gomantics/sx/sx.go:209:	WithNormalize			100.0%
github.com/gomantics/sx/sx.go:221:	PascalCase			92.9%
github.com/gomantics/sx/sx.go:249:	lowercaseWord			83.3%
github.com/gomantics/sx/sx.go:263:	CamelCase			93.3%
github.com/gomantics/sx/sx.go:293:	KebabCase			66.7%
github.com/gomantics/sx/sx.go:317:	SnakeCase			100.0%
github.com/gomantics/sx/sx.go:322:	TrainCase			64.3%
github.com/gomantics/sx/sx.go:348:	FlatCase			100.0%
github.com/gomantics/sx/sx.go:353:	UpperFirst			0.0%
github.com/gomantics/sx/sx.go:358:	LowerFirst			0.0%
total:					(statements)			88.7%