Add commitments to sparse polynomials in KZG

[mariuslp]

Description

This PR adds the method commit_sparse to the KZG10 module. Its API is equivalent to the one of commit but accepts sparse polynomials instead of dense polynomials.
This optimisation allows to replace the MSM by a naive version, which in the case of sparse polynomials such as X^n - 1, X - alpha etc. is order of magnitudes faster. This can significantly reduce verifier time.

Important note: this PR can only be merged after the merge of arkworks-rs/algebra#1035.

Results from a quick benchmark, where the verifier checks if e(comm, h) = e(comm, h) for some point h from the SRS:

Comm = X^n - 1
commit time is down by 64.7%, total verifier time (1 commit + 2 pairings) is down by 32.7%

Comm = X - alpha
commit time is down by 75.0%, total verifier time (1 commit + 2 pairings) is down by 17.8%

Comm = X^(n-k)
commit time is down by 99.7%, total verifier time (1 commit + 2 pairings) is down by 27.6%

closes: #169

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[Pratyush]

Looks good, thanks!