Implement protocol to create cross-shard coordinated randomness

[akoshelev]

This protocol will generate random seeds using PRSS and then distribute those seeds to all shards. Every shard will initialize cross-shard PRSS from those seeds. Follows up on #1410.

[eriktaubeneck]

is this supposed to integrate with ShardBinding::cross_shard_prss? If so, it's not obvious how that happens.

otherwise, looks good (other than a test issue to resolve)

[akoshelev]

Is this supposed to integrate with ShardBinding::cross_shard_prss? If so, it's not obvious how that happens.

yes, this will be used in real world implementation to initialize PRSS instances on different shards. I am working on sharded shuffle implementation that will make use of it

[codecov]

Codecov Report

Attention: Patch coverage is 96.38554% with 6 lines in your changes missing coverage. Please review.

Project coverage is 93.40%. Comparing base (e6e08af) to head (619b442).
Report is 36 commits behind head on main.

Files with missing lines	Patch %	Lines
ipa-core/src/helpers/cross_shard_prss.rs	90.32%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1426      +/-   ##
==========================================
+ Coverage   93.29%   93.40%   +0.11%     
==========================================
  Files         224      227       +3     
  Lines       38602    39149     +547     
==========================================
+ Hits        36014    36569     +555     
+ Misses       2588     2580       -8     

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