Proof of storage

[martyall]

• add opening proof
• add verification for opening proof
• add test

depends on #2967

[codecov]

Codecov Report

Attention: Patch coverage is 72.64957% with 32 lines in your changes missing coverage. Please review.

Please upload report for BASE (martin/saffron-store-commitments-in-blob@cb4c09c). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
saffron/src/env.rs	55.26%	17 Missing ⚠️
saffron/src/main.rs	0.00%	14 Missing ⚠️
saffron/src/proof.rs	97.50%	1 Missing ⚠️

Additional details and impacted files

@@                             Coverage Diff                             @@
##             martin/saffron-store-commitments-in-blob    #2968   +/-   ##
===========================================================================
  Coverage                                            ?   76.92%           
===========================================================================
  Files                                               ?      262           
  Lines                                               ?    61355           
  Branches                                            ?        0           
===========================================================================
  Hits                                                ?    47198           
  Misses                                              ?    14157           
  Partials                                            ?        0           

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