Update Cargo.lock and improve mgm benches

[newpavlov]

Previously MGM decrypt was always failing, so we were measuring only tag verification without decryption.

[codecov-commenter]

Codecov Report

Merging #357 (5a1fbdd) into master (5709f1b) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #357   +/-   ##
=======================================
  Coverage   89.24%   89.24%           
=======================================
  Files          39       39           
  Lines        1888     1888           
=======================================
  Hits         1685     1685           
  Misses        203      203           

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