Improve documentation, add examples, and modernize CI workflows

[google-labs-jules]

This PR addresses several maintenance tasks:

1. Examples: Added example_test.go with testable examples for the main API functions (ToCamelCase, ToPascalCase, ToKebabCase, ToSnakeCase, ToFormattedCase).
2. Documentation: Improved godoc comments in types.go and updated README.md with build status badges and license information.
3. License: Added an MIT LICENSE file.
4. CI/CD:
   • Renamed go.yml to test.yml and updated actions/setup-go to v5.
   • Created vet.yml for go vet.
   • Created golangci-lint.yml for linting.
   • Created fmt.yml to enforce code formatting.
5. Formatting: Ran go fmt which slightly updated types_test.go.

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PR created automatically by Jules for task 1352783081704879614 started by @arran4

[google-labs-jules]

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