Use YARA for batched word matching

[liquidsec]

Summary

• Adds baddns/lib/yara_helper.py — standalone YARA helper for compiling and matching rules
• Adds WordMatcher class to matcher.py that compiles all 98 word matchers across signatures into a single YARA ruleset at load time
• One YARA match() call per HTTP response replaces 98 separate word in text substring scans
• Matcher.is_match() accepts pre-computed YARA results via word_results/sig_idx params, falls back to original behavior when not provided (backward compatible)
• BadDNS_base accepts optional word_matcher kwarg; CLI builds it once after load_signatures()
• Adds yara-python>=4.5.0 dependency
• Corresponding bbot-side change (build WordMatcher in setup(), pass to modules) will be in a separate bbot PR

Benchmarked at ~1.7x end-to-end speedup.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 77.06422% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.75%. Comparing base (2a62b5d) to head (221a71a).

Files with missing lines	Patch %	Lines
baddns/lib/yara_helper.py	23.07%	20 Missing ⚠️
baddns/lib/matcher.py	92.30%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #903      +/-   ##
==========================================
- Coverage   99.94%   98.75%   -1.20%     
==========================================
  Files          27       28       +1     
  Lines        1977     2082     +105     
==========================================
+ Hits         1976     2056      +80     
- Misses          1       26      +25     

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