Reduce RST cancel prefix to 32 bytes

[puddly]

40 bytes for some reason is inconsistent upon more thorough testing, 32 does not have this problem.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.55%. Comparing base (1ad5b57) to head (b91f921).
⚠️ Report is 1 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #697   +/-   ##
=======================================
  Coverage   99.55%   99.55%           
=======================================
  Files          58       58           
  Lines        4054     4054           
=======================================
  Hits         4036     4036           
  Misses         18       18           

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