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/files.py

@@ -1,26 +1,34 @@
 from __future__ import annotations
 
 import re
-from urllib.parse import unquote
 import os
+from urllib.parse import unquote
 
 from .cookies import get_cookies_dir
 
-def secure_filename(filename: str) -> str:
+
+def secure_filename(filename: str, max_length: int = 100) -> str:
+    """Sanitize a filename for safe filesystem storage."""
     if filename is None:
         return None
-    # Keep letters, numbers, basic punctuation and all Unicode chars
+
+    # Keep letters, numbers, basic punctuation, underscores
     filename = re.sub(
-        r'[^\w.,_+-]+',
-        '_',
+        r"[^\w.,_+\-]+",
+        "_",
         unquote(filename).strip(),
         flags=re.UNICODE
     )
-    encoding = 'utf-8'
-    max_length = 100
+    encoding = "utf-8"
     encoded = filename.encode(encoding)[:max_length]
-    decoded = encoded.decode(encoding, 'ignore')
+    decoded = encoded.decode(encoding, "ignore")
     return decoded.strip(".,_+-")
 
-def get_bucket_dir(*parts):
-    return os.path.join(get_cookies_dir(), "buckets", *[secure_filename(part) for part in parts if part])
+
+def get_bucket_dir(*parts: str) -> str:
+    """Return a path under the cookies 'buckets' directory with sanitized parts."""
+    return os.path.join(
+        get_cookies_dir(),
+        "buckets",
+        *[secure_filename(part) for part in parts if part]
+    )