added IOnChainAllocation interface

[mgretzke]

Added an IOnChainAllocation interface that allows incoming calls to create an allocation via allocateFor, if the caller can prove the sponsors intention by either providing a valid signature, or the derived claimHash was registered in the compact.
To receive the nonce that will be used within the verification, you can call requestNonce

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.39%. Comparing base (b9c3b54) to head (714f29e).

Additional details and impacted files

@@           Coverage Diff           @@
##               v1     #154   +/-   ##
=======================================
  Coverage   98.39%   98.39%           
=======================================
  Files          41       41           
  Lines        1805     1805           
  Branches       98       98           
=======================================
  Hits         1776     1776           
  Misses         29       29           

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