Use default salt length for PS256/384/512 instead of max salt length.

[dajiaji]

Fix #195.

[codecov]

Codecov Report

Merging #196 (6cf92f7) into main (8bfb97f) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #196   +/-   ##
=======================================
  Coverage   99.84%   99.84%           
=======================================
  Files          28       28           
  Lines        2608     2612    +4     
  Branches      710      710           
=======================================
+ Hits         2604     2608    +4     
  Misses          4        4           

Impacted Files	Coverage Δ
cwt/algs/rsa.py	100.00% <100.00%> (ø)

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