refactor(extractor): reduce code duplication and improve PEP8 compliance

[michaelos443]

Summary

This PR refactors the extractor.py module to reduce code duplication, improve docstring clarity, and ensure PEP8 compliance.

Changes

Code Duplication Reduction

• _init_base_attributes() - Helper function to consolidate common initialization logic shared between Extractor and VideoExtractor classes
• _get_stream() - Centralizes logic for retrieving stream info from either streams or dash_streams
• _run_download() - Consolidates the nearly identical code from download_by_url and download_by_vid
• _sort_streams() - Extracts the complex stream sorting logic
• _get_stream_id_key() - Eliminates the repeated stream['id'] if 'id' in stream else stream['itag'] pattern
• _select_best_stream_id() - Extracts best stream selection logic
• _save_auxiliary_files() - Consolidates danmaku and lyrics file saving

PEP8 Compliance

• Fixed all lines exceeding 79 characters
• Changed bare except: to specific except KeyError:
• Removed commented-out code
• Removed unused imports (match1, get_content)

Docstring Improvements

• Added comprehensive module docstring
• Added class docstrings with attribute documentation
• Added method docstrings with Args and Returns sections
• Used Google-style docstring format consistently

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Pull Request opened by Augment Code with guidance from the PR author