Add backtrack protection to 6.x

[blakeembrey]

Closes #323. It will likely break some existing routes around the edge cases, but it should eliminate the vulnerability when the pattern isn't specified.

[codecov]

Codecov Report

Attention: Patch coverage is 41.66667% with 28 lines in your changes missing coverage. Please review.

Project coverage is 95.61%. Comparing base (28a5b27) to head (a1cfa60).

Files with missing lines	Patch %	Lines
redos.ts	0.00%	20 Missing and 1 partial ⚠️
src/index.ts	74.07%	7 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##               6.x     #324      +/-   ##
===========================================
- Coverage   100.00%   95.61%   -4.39%     
===========================================
  Files            1        2       +1     
  Lines          621      662      +41     
  Branches       140      145       +5     
===========================================
+ Hits           621      633      +12     
- Misses           0       28      +28     
- Partials         0        1       +1     

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