feat: Enhance type annotations and logging transparency

Comprehensive improvements to type annotations and logging to make
slurminade more transparent and IDE-friendly.

## Type Annotation Improvements

### conf.py - 100% Type Coverage
- Add complete type annotations to all functions
- Add parameter types for all optional parameters
- Add return types to all functions
- Add docstrings with Args/Returns sections

### dispatcher.py - Enhanced Types
- Add return type to _log_dispatch()
- Add module-level logger for performance
- Improve type hints for key functions

## Logging Improvements

### Transparency Goals
- Log all configuration changes (DEBUG + INFO levels)
- Log dispatcher selection and changes (INFO level)
- Log task dispatching with details (INFO level)
- Use lazy formatting for performance

### conf.py - Comprehensive Logging
- DEBUG: Configuration file loading
- INFO: Configuration updates with key counts
- DEBUG: Detailed configuration values
- ERROR: Configuration loading failures
- INFO: Summary of loaded configuration

### dispatcher.py - Enhanced Logging
- INFO: Dispatcher selection (Slurm vs. local)
- DEBUG: Dispatcher creation
- WARNING: Slurm not available
- INFO: Manual dispatcher changes
- Fixed: Use lazy formatting instead of f-strings

## Benefits

### For Users
- See exactly what slurminade is doing
- Debug configuration issues easily
- Understand dispatcher selection
- Track job submissions in real-time

### For Developers
- IDE autocomplete with correct types
- Early error detection before runtime
- Inline documentation on hover
- Safe automated refactoring

### For Maintainers
- Self-documenting code
- Type safety prevents bugs
- Better user bug reports with logs
- Performance improvements (lazy logging)

## Performance
- Lazy logging: No string construction if logging disabled
- Cached loggers: Faster logging calls
- No runtime overhead when logging off

## Testing
- All 36 tests pass
- No regressions
- Backward compatible

All changes maintain full backward compatibility.

Author: claude