feat: Add weak reference and one-shot connection support

[san-tekart]

• Add weak reference support via weak=True in signal connections
• Add one-shot connections via one_shot=True that auto-disconnect after first emit
• Improve thread safety with internal connection locking
• Add extensive documentation for all public APIs
• Add new tests for weak references and one-shot functionality
• Update examples and documentation to demonstrate new features

This commit introduces two major features:

1. Weak reference support allows receivers to be garbage collected
2. One-shot connections automatically disconnect after first successful emit

The changes also include significant documentation improvements and additional test coverage.