Add comprehensive documentation throughout the codebase

[Copilot]

This PR adds comprehensive documentation to all exported types, functions, and variables in the waitfor package to improve developer experience and adherence to Go documentation standards.

Changes Made

Package-Level Documentation

Added detailed package documentation explaining:

• Purpose and use cases for the waitfor library
• Plugin-based architecture for resource types
• Retry mechanisms with exponential backoff
• Practical usage examples with code snippets

Type Documentation

Documented all exported types with detailed explanations:

• Program: Command execution structure with resource dependencies
• Runner: Main component for resource testing and program execution
• Registry: Resource factory management and URL scheme mapping
• Resource: Interface definition with implementation guidelines
• ResourceConfig: Plugin configuration structure
• ResourceFactory: Function type for creating resource instances
• Options: Configuration parameters for retry behavior
• Module: Plugin function type enabling extensible resource support

Function Documentation

Enhanced all exported functions with comprehensive documentation:

• New(): Constructor with configuration examples
• Test(): Resource availability testing with detailed parameter explanations
• Run(): Combined resource testing and program execution workflow
• Register(): Adding custom resource factories
• Resolve(): URL-to-resource conversion process
• WithInterval(), WithMaxInterval(), WithAttempts(): Configuration options with usage examples

Error Documentation

Added proper documentation for exported error variables:

• ErrWait: Resource availability failure conditions
• ErrInvalidArgument: Invalid parameter scenarios

Documentation Standards

All documentation follows Go conventions:

• Complete sentences with proper punctuation
• Practical code examples where applicable
• Clear parameter and return value explanations
• Context-aware implementation guidance

Verification

• Code builds and all tests pass
• Linting passes with no documentation-related issues
• Documentation is accessible via go doc at package, type, and function levels
• Examples are syntactically correct and demonstrate real usage patterns

The enhanced documentation makes the library more accessible to developers and provides clear guidance for implementing custom resource types and integrating the library into applications.

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