rust -> edition 2021 and version 1.56.0

[mimoo]

see https://twitter.com/m_ou_se/status/1451280992489164800

[codecov-commenter]

Codecov Report

Merging #198 (eb974f1) into master (f891be5) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #198      +/-   ##
==========================================
- Coverage   88.52%   88.52%   -0.01%     
==========================================
  Files          73       73              
  Lines       17536    17534       -2     
==========================================
- Hits        15524    15522       -2     
  Misses       2012     2012              

Impacted Files	Coverage Δ
dlog/plonk/src/index.rs	88.73% <0.00%> (-1.55%)	⬇️
dlog/plonk-15-wires/src/index.rs	97.14% <0.00%> (+0.91%)	⬆️

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[mimoo]

rebased