feat(resharding) - Make shard ids non-contiguous - part 2

[wacban]

More of the same. I added a rust feature to quickly switch between the old and new shard ids to speed up work.

No interesting changes here, just syntax everywhere. I hope.

[codecov]

Codecov Report

Attention: Patch coverage is 98.13084% with 2 lines in your changes missing coverage. Please review.

Project coverage is 71.74%. Comparing base (2b022a6) to head (5059462).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
core/primitives/src/shard_layout.rs	98.00%	0 Missing and 1 partial ⚠️
core/primitives/src/trie_key.rs	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #12209      +/-   ##
==========================================
- Coverage   71.74%   71.74%   -0.01%     
==========================================
  Files         825      825              
  Lines      165819   165868      +49     
  Branches   165819   165868      +49     
==========================================
+ Hits       118973   119008      +35     
- Misses      41650    41663      +13     
- Partials     5196     5197       +1     

Flag	Coverage Δ
backward-compatibility	0.17% <0.00%> (-0.01%)	⬇️
db-migration	0.17% <0.00%> (-0.01%)	⬇️
genesis-check	1.26% <7.93%> (+<0.01%)	⬆️
integration-tests	38.92% <49.53%> (+0.01%)	⬆️
linux	71.43% <98.13%> (+<0.01%)	⬆️
linux-nightly	71.32% <98.13%> (-0.01%)	⬇️
macos	54.35% <96.26%> (+0.08%)	⬆️
pytests	1.57% <7.93%> (+<0.01%)	⬆️
sanity-checks	1.38% <0.00%> (-0.01%)	⬇️
unittests	65.52% <97.19%> (+0.01%)	⬆️
upgradability	0.21% <0.00%> (-0.01%)	⬇️

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