⚡ Limit concurrency in NovelFireSource to prevent rate limiting

[Aatricks]

💡 What:

• Implemented Semaphore(3) in NovelFireSource.loadAdditionalChapterPages to limit concurrent network requests.
• Added NovelFireSourceConcurrencyTest to verify the concurrency limit using a mocked OkHttpClient interceptor.

🎯 Why:

• Previously, loadAdditionalChapterPages would spawn a coroutine for every page (2..maxPage) simultaneously. For novels with many pages, this resulted in a burst of requests (unbounded concurrency) which could overwhelm the server or the client's network stack.
• Limiting concurrency to 3 ensures a steady, respectful flow of requests.

📊 Measured Improvement:

• Baseline: NovelFireSourceConcurrencyTest showed a max concurrency of 9 for a 10-page novel (all pages requested at once).
• Optimized: NovelFireSourceConcurrencyTest confirms max concurrency is now limited to <= 5 (specifically constrained by Semaphore(3)).

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PR created automatically by Jules for task 3166179376735314383 started by @Aatricks

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