fix: improve rxRequest API ergonomics with function overloads

[michaelbe812]

Summary

• Implements function overloads for rxRequest to improve API ergonomics
• Eliminates unsafe type casting when no trigger is provided
• Provides better type safety and developer experience

Related Issue

Fixes #53

Changes Made

API Improvements

• Added two distinct function overloads:
  • No-trigger case: requestFn: () => Observable
  • With-trigger case: requestFn: (arg: A) => Observable
• Created separate type definitions for each overload scenario
• Removed unsafe 'undefined as A' type casting from implementation

Type Safety

• Proper type inference for both usage patterns
• No more forced parameters that aren't actually used
• Clean separation of concerns between triggered and non-triggered requests

Testing

• Added comprehensive tests for both overload cases
• Verified type inference works correctly
• All existing tests pass, confirming backward compatibility
• Added 3 new test cases specifically for overload type safety

Breaking Changes

None - this change is fully backward compatible. It only adds function overloads without removing any existing functionality.

Testing Checklist

• All existing tests pass
• New tests added for overloads
• Type checking passes
• Linting passes
• Test suite passes