Add log level resetting functionality for FFI

[konard]

Summary

Implements log level resetting functionality for FFI as requested in issue #12. The solution uses tracing_subscriber::reload::Handle with a global lazy static handle to provide dynamic log level management.

Key Features

• Global reload handle: Uses once_cell::Lazy with Mutex<Option<reload::Handle>> to store the reload handle globally
• Dynamic log level control: New FFI functions set_log_level() and reset_log_level() allow runtime log level changes
• Thread-safe implementation: Uses mutex protection for the global handle
• Comprehensive error handling: Proper validation and error reporting for invalid log levels
• Backward compatibility: Maintains existing logging functionality while adding new features

Implementation Details

New FFI Functions

• set_log_level(level: *const c_char) -> bool: Sets log level to specified string (e.g., "trace", "debug", "info", "warn", "error")
• reset_log_level() -> bool: Resets log level to "trace" (maximum verbosity)

Dependencies Updated

• Updated tracing-subscriber to version 0.3.18 (provides reload functionality)
• Added once_cell 1.19 for thread-safe lazy static initialization

Core Changes

• Modified setup_shared_logger() to use reloadable filter with reload::Layer
• Added global RELOAD_HANDLE static variable for handle management
• Enhanced subscriber setup to use Registry with layered architecture

Test Coverage

Added comprehensive tests covering:

• ✅ Basic log level changing functionality
• ✅ Log level reset functionality
• ✅ Invalid log level handling
• ✅ Null pointer safety
• ✅ Error conditions and edge cases

Usage Example

// C/C++ usage
bool success = set_log_level("info");  // Set to info level
success = reset_log_level();           // Reset to trace level

Technical Notes

The implementation avoids the issues mentioned in the original issue regarding generic types in statics by using a type-erased approach with Box<dyn> and once_cell::Lazy instead of raw lazy_static. This provides a clean, thread-safe solution that works with the current tracing ecosystem.

🤖 Generated with Claude Code

Fixes #12