Add padding and proving for smaller programs

[martyall]

Builds on #2910 and uses the no-op selector to do the padding.

You can run against any test mips program using

 RUST_LOG=debug ./o1vm/test-mips-program-prover.sh o1vm/resources/programs/mips/bin/nor srs/test_vesta.srs

where you can replace nor with any test mips program (except the oracle programs, see #2944) . I didn't add this to CI, but we can if we want.

[codecov]

Codecov Report

Attention: Patch coverage is 3.70370% with 78 lines in your changes missing coverage. Please review.

Project coverage is 76.54%. Comparing base (54a9e0c) to head (3c77506).

Files with missing lines	Patch %	Lines
o1vm/src/pickles/main.rs	0.00%	72 Missing ⚠️
o1vm/src/interpreters/mips/witness.rs	33.33%	6 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           dw/no-op    #2956      +/-   ##
============================================
- Coverage     76.60%   76.54%   -0.06%     
============================================
  Files           255      255              
  Lines         61066    61112      +46     
============================================
  Hits          46781    46781              
- Misses        14285    14331      +46     

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