Add missing type annotations to core library method signatures

[dereuromark]

Summary

• Adds proper type annotations to method signatures across 8 core library documentation files
• Aligns signatures with actual CakePHP 5.x source code
• Covers approximately 50+ method signatures total

Files updated:

• app.md: className() - added string types for parameters
• collections.md: ~33 methods - full type annotations (callable, string, int, mixed, etc.)
• email.md: setAttachments(), setEmailPattern() - added parameter types and return types
• inflector.md: 10 methods - verified types match source
• number.md: setDefaultCurrency() - changed to static and added nullable string type
• text.md: transliterate(), toList() - verified types match source
• time.md: 8 methods - added Closure/array/string/int types for format params, bool returns for comparison methods
• xml.md: build(), toArray() - verified types match source

Test plan

• Verify documentation renders correctly
• Spot check a few method signatures against CakePHP 5.x source

Refs #7744