Misc crypto micro-benchmarks

[ctz]

Pulling these out of #1414 in case they are useful for measuring #1508 performance difference.

[codecov]

Codecov Report

Merging #1511 (812c2d3) into main (4d3f303) will increase coverage by 0.00%.
Report is 3 commits behind head on main.
The diff coverage is 95.56%.

@@           Coverage Diff           @@
##             main    #1511   +/-   ##
=======================================
  Coverage   96.46%   96.46%           
=======================================
  Files          72       74    +2     
  Lines       15105    15107    +2     
=======================================
+ Hits        14571    14573    +2     
  Misses        534      534           

Files	Coverage Δ
rustls/src/crypto/ring/mod.rs	100.00% <ø> (+4.16%)	⬆️
rustls/src/crypto/ring/sign.rs	96.00% <ø> (ø)
rustls/src/tls12/mod.rs	97.85% <ø> (ø)
rustls/src/crypto/ring/kx.rs	97.05% <97.05%> (ø)
rustls/src/crypto/ring/ticketer.rs	95.16% <95.16%> (ø)

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