Encode/Decode to polynomials in monomial basis

[martyall]

Changes

• encode/decode to polynomials in coefficient form (previously used only field elems)
• add large randomized test to CI

Example

I ran the test script locally on a 500mb json file and got the following output

2025-01-22T18:53:21.081Z DEBUG saffron: Encoding file domain_size=65536 input_file="/home/martyall/tmp/fork_config.json"
2025-01-22T18:53:25.159Z DEBUG encode: saffron::serialization: Encoded 528127993 bytes into 260 polynomials
2025-01-22T18:53:25.206Z  INFO encode: saffron::serialization: close time.busy=3.77s time.idle=5.37µs
2025-01-22T18:53:25.206Z DEBUG saffron: Writing encoded blob to file output_file="/home/martyall/tmp/fork_config.bin"
2025-01-22T18:53:26.415Z DEBUG saffron: Decoding file domain_size=65536 input_file="/home/martyall/tmp/fork_config.bin"
2025-01-22T18:53:31.173Z  INFO decode: saffron::serialization: close time.busy=3.52s time.idle=3.97µs
2025-01-22T18:53:31.173Z DEBUG saffron: Writing decoded blob to file output_file="/home/martyall/tmp/fork_config-decodedjson"

So both encode/decode for 500MB takes about 3.5 seconds (not including file I/O). This seems like a reasonable speed for getting this demo off the ground.

[codecov]

Codecov Report

Attention: Patch coverage is 49.01961% with 26 lines in your changes missing coverage. Please review.

Project coverage is 76.85%. Comparing base (70732bc) to head (fe10025).
Report is 6 commits behind head on master.

Files with missing lines	Patch %	Lines
saffron/src/main.rs	0.00%	14 Missing ⚠️
saffron/src/serialization.rs	73.52%	9 Missing ⚠️
saffron/src/cli.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2959      +/-   ##
==========================================
+ Coverage   76.79%   76.85%   +0.06%     
==========================================
  Files         258      258              
  Lines       61166    61202      +36     
==========================================
+ Hits        46971    47036      +65     
+ Misses      14195    14166      -29     

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