[Feature] Update Logging

[dfop02]

Description

Problem

All warnings were emitted via the root logger (logging.warning(...)), making it impossible for consumers to silence or configure html4docx output without affecting their entire application logging.

Changes

Logging overhaul

• Added logger = logging.getLogger(__name__) to h4d.py, utils.py, and metadata.py
• A single NullHandler on the package root (__init__.py) keeps the library silent by default — no handler needed per-module
• Replaced all logging.<level>(...) and print(...) warning calls with logger.<level>(...) across all three modules
• Downgraded "Unrecognized CSS style" messages from WARNING → DEBUG (expected skips for any real-world HTML, not actionable problems)

Tests

• Updated test_custom_style_not_found_warning to assert against the named logger html4docx.h4d
• Migrated test_metadata.py warning tests from capsys (stdout) → caplog (named logger)
• Added tests verifying logger names, NullHandler placement, and that warnings are silenceable per-logger

Docs

• Added a Logging section to README.md with recipes for silencing output in plain Python, Django LOGGING dict, and enabling debug-level detail

Linter

• Fixed all 14 outstanding ruff offenses (SIM118, SIM401, SIM102, SIM201, SIM108, UP031, B905, B011)

Result

Consumers can now silence all html4docx output with a single config entry:

# Django LOGGING dict
"html4docx": {"level": "ERROR", "propagate": False}

# or plain Python
logging.getLogger("html4docx").setLevel(logging.ERROR)

Issue Reference

Fixes #80

Checklist Before Requesting a Review

• I have performed a self-review of my code.
• My code follows the project's coding style and guidelines.
• I have run tests and verified that all existing and new tests pass.
• I have added new tests to cover my changes.