Poly-commitment: rename elems field into chunks

[dannywillems]

It is more meaningful because it is actually chunks. In following pull requests, the abstraction over PolyComm will be changed, to avoid erroneous usage of PolyComm.

It is part of the implementation of the prover into pickles, as I noticed I made a small error while splitting the quotient polynomial in chunks.

I am breaking the usage of PolyComm in develop, and in Mina, cc @volhovm as you will work on merging develop into master for proof-systems.

[codecov]

Codecov Report

Attention: Patch coverage is 85.81081% with 21 lines in your changes missing coverage. Please review.

Project coverage is 72.98%. Comparing base (7751b57) to head (7f9f96c).
Report is 25 commits behind head on master.

Files with missing lines	Patch %	Lines
poly-commitment/src/commitment.rs	81.63%	9 Missing ⚠️
ivc/src/plonkish_lang.rs	0.00%	3 Missing ⚠️
ivc/src/prover.rs	0.00%	3 Missing ⚠️
poly-commitment/src/ipa.rs	87.50%	2 Missing ⚠️
arrabiata/src/witness.rs	87.50%	1 Missing ⚠️
folding/src/lib.rs	90.90%	1 Missing ⚠️
kimchi/src/verifier.rs	50.00%	1 Missing ⚠️
o1vm/src/legacy/trace.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2658   +/-   ##
=======================================
  Coverage   72.98%   72.98%           
=======================================
  Files         244      244           
  Lines       57768    57777    +9     
=======================================
+ Hits        42162    42170    +8     
- Misses      15606    15607    +1     

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[querolita]

Approving, but let's make sure the mina side is not broken if trying to access elems

[dannywillems]

Approving, but let's make sure the mina side is not broken if trying to access elems

It will be broken.

[dannywillems]

Approving, but let's make sure the mina side is not broken if trying to access elems

It will be broken.

I've checked to backport in develop by cherry-picking, and update Mina accordingly, but proof-systems develop/master are unsynced. I think @volhovm is working on this.

[dannywillems]

I'm taking the responsibility to introduce this breaking change. If you have difficulties when merging develop into master @volhovm, I think it is fair for me to help you to propagate this change in mina + o1js.