Further limits on expensive path building

[ctz]

This is intended to be complementary to #160 and addresses briansmith/webpki#276 in the same manner as NSS libmozpkix.

[codecov]

Codecov Report

Merging #163 (1af0ee0) into main (659167f) will increase coverage by 0.06%.
The diff coverage is 87.95%.

@@            Coverage Diff             @@
##             main     #163      +/-   ##
==========================================
+ Coverage   96.56%   96.62%   +0.06%     
==========================================
  Files          15       15              
  Lines        4364     4480     +116     
==========================================
+ Hits         4214     4329     +115     
- Misses        150      151       +1     

Files Changed	Coverage Δ
src/error.rs	54.90% <37.50%> (-0.21%)	⬇️
src/verify_cert.rs	97.83% <100.00%> (+0.50%)	⬆️

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[cpu]

This looks great, thank you for tidying up some of the surrounding code. I peeked at the diff coverage dip and it's specific to the error ranking changes (which are much appreciated).