⚡ Bolt: Cache RegExp in parsing adapters

[JustLookAtNow]

💡 What:
Extracted RegExp object instantiations from inline usage inside NexusPHPWebAdapter and NexusPHPAdapter into top-level final variables.

🎯 Why:
In Dart, compiling regular expressions carries a performance cost. The NexusPHPWebAdapter compiles these inside a background isolate (during HTML parsing for torrent lists), and NexusPHPAdapter compiles a whitespace RegExp repeatedly inside nested loops traversing API data. Re-instantiating identical regular expressions on these hot paths results in unnecessary object allocations and CPU overhead, especially given that Dart isolate memory is discrete and requires local compilation.

📊 Impact:
Eliminates redundant RegExp compilation during list parsing and category iteration, reducing execution time and object churn.

🔬 Measurement:
Verification includes running standard Dart format, linter, and flutter test to ensure functional parity. Performance improvement can be observed in reduced parse times during operations like parseSearchResults in test/benchmark_parsing.dart.

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PR created automatically by Jules for task 14770700081820352521 started by @JustLookAtNow

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