Implement Plonky3 frontend adaptor

[ed255]

Plonky3 frontend implementation. Allows using a circuit defined with the Air trait from plonky3 to be proved with a halo2 backend.

Bump rust version from 1.73.0 to 1.75.0 because plonky3 requires it.

[ed255]

I just made this PR ready for review to get some feedback. There are some TODOs in the code but the main logic is working.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 95.93095% with 33 lines in your changes are missing coverage. Please review.

Project coverage is 81.84%. Comparing base (87fb07f) to head (37c916f).

Files	Patch %	Lines
p3_frontend/src/lib.rs	94.00%	15 Missing :warning:
p3_frontend/src/symbolic_expression.rs	95.33%	11 Missing :warning:
p3_frontend/src/fwrap.rs	97.68%	5 Missing :warning:
halo2_backend/src/helpers.rs	0.00%	1 Missing :warning:
p3_frontend/src/symbolic_builder.rs	97.14%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #306      +/-   ##
==========================================
+ Coverage   80.86%   81.84%   +0.97%     
==========================================
  Files          80       82       +2     
  Lines       16567    17000     +433     
==========================================
+ Hits        13397    13913     +516     
+ Misses       3170     3087      -83     

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[ed255]

I've added unit tests and increased the test coverage to ~90% The only file that doesn't have unit tests is the p3_frontend/src/lib.rs, but most of it is covered by the fibonacci and keccak tests. Nevertheless I may add unit tests for that in the future.