feat: E-Hentai metadata provider initial implementation

[wiseCirno]

Description

Add metadata provider for E-Hentai.

I tried my best to mimic the implementation style and architecture of the existing providers (like Bangumi and Hentag) to maintain consistency across the codebase, though there might still be some slight deviations.

What is working

• Automatic metadata matching is fully functional. (While Manual Identification works reliably, Auto-Identify currently only matches a small subset of the library. I need to investigate the underlying logic of the auto-match feature further.)
• Manual metadata identification/searching works as expected.
• Parses metadata including titles (original & translated), authors/groups, tags (with namespaces properly cleaned) and covers.

Known Limitations & Notes

• Configuration: Currently, this provider can only be configured manually by modifying the configuration file. It is not yet recognized or selectable via the Web UI extension.
• Rate Limiting: I have implemented a rate limiter based on the official E-Hentai API guidelines (4 requests per 5 seconds) with some redundancy. However, please note that during an extreme stress test (auto-matching around 800 series continuously), I still eventually triggered their rate limit. Normal daily usage should be perfectly fine.
• Regex Patterns: The current regex is only partially effective. I am working on a more general-purpose regex by analyzing a wider variety of doujinshi naming conventions.

Personal Doujinshi Library Organize Format

<library_name>/<doujinshi_title>/<doujinshi_title>.<file_extension>

Please let me know if there is anything that needs to be changed or improved. Thanks for reviewing!