rtp: cache regexes in memory for reuse

[adamdecaf]

Fixes: #45

[codecov-commenter]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (957ae88) 84.86% compared to head (94a6826) 85.49%.

❗ Current head 94a6826 differs from pull request most recent head 36c4c28. Consider uploading reports for the commit 36c4c28 to get more accurate results

Files	Patch %	Lines
pkg/rtp/restrictions.go	83.33%	1 Missing and 1 partial ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master      #46      +/-   ##
==========================================
+ Coverage   84.86%   85.49%   +0.62%     
==========================================
  Files          12       12              
  Lines         185      193       +8     
==========================================
+ Hits          157      165       +8     
  Misses         24       24              
  Partials        4        4              

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[jerome-laforge]

LGTM

Thx!