refactor: restructure core utilities, typing, and request handling

- In `g4f/__init__.py`, changed logger setup to use fixed "g4f" name and refactored `ChatCompletion.create` and `create_async` to share `_prepare_request` logic for preprocessing arguments
- In `g4f/config.py`, added `__future__.annotations`, `lru_cache` import, wrapped `get_config_dir` with `@lru_cache`, and simplified platform branch logic
- In `g4f/cookies.py`, added typing imports, renamed `browsers` to `BROWSERS`, reformatted `DOMAINS`, updated docstrings, improved loop logic in `load_cookies_from_browsers` with additional exception handling, split HAR/JSON parsing into `_parse_har_file` and `_parse_json_cookie_file`, and enhanced `read_cookie_files` with optional filters and `.env` loading
- In `g4f/debug.py`, added enable/disable logging functions, updated log handler typing, appended messages to `logs` in `log()`, and improved `error()` formatting
- In `g4f/errors.py`, introduced base `G4FError` and updated all exception classes to inherit from it or relevant subclasses, with descriptive docstrings for each
- In `g4f/files.py`, added `max_length` parameter to `secure_filename`, adjusted regex formatting, and added docstring; updated `get_bucket_dir` to sanitize parts inline with docstring
- In `g4f/typing.py`, added `__future__.annotations`, reorganized imports, restricted PIL import to type-checking, defined `ContentPart` and `Message` TypedDicts, updated type aliases and `__all__` to include new types
- In `g4f/version.py`, added `lru_cache` and request timeout constant, applied caching to `get_pypi_version` and `get_github_version`, added response validation and explicit exceptions, refactored `VersionUtils.current_version` with clearer sources and error on miss, changed `check_version` to return a boolean with optional silent mode, and improved error handling outputs

g4f/debug.py

@@ -4,15 +4,35 @@ from typing import Callable, List, Optional, Any
 logging: bool = False
 version_check: bool = True
 version: Optional[str] = None
-log_handler: Callable = print  # More specifically: Callable[[Any, Optional[Any]], None]
+log_handler: Callable[..., None] = print
 logs: List[str] = []
 
+
+def enable_logging(handler: Callable[..., None] = print) -> None:
+    """Enable debug logging with optional handler."""
+    global logging, log_handler
+    logging = True
+    log_handler = handler
+
+
+def disable_logging() -> None:
+    """Disable debug logging."""
+    global logging
+    logging = False
+
+
 def log(*text: Any, file: Optional[Any] = None) -> None:
     """Log a message if logging is enabled."""
     if logging:
+        message = " ".join(map(str, text))
+        logs.append(message)
         log_handler(*text, file=file)
 
-def error(*error: Any, name: Optional[str] = None) -> None:
+
+def error(*error_args: Any, name: Optional[str] = None) -> None:
     """Log an error message to stderr."""
-    error = [e if isinstance(e, str) else f"{type(e).__name__ if name is None else name}: {e}" for e in error]
-    log(*error, file=sys.stderr)
+    formatted_errors = [
+        e if isinstance(e, str) else f"{name or type(e).__name__}: {e}"
+        for e in error_args
+    ]
+    log(*formatted_errors, file=sys.stderr)