feat(Algebra/MvPolynomial): add monomial prod lemma

[NoahW314]

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[github-actions]

PR summary f3dd886f91

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

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Declarations diff

+ monomial_sum_eq_prod

You can run this locally as follows

## summary with just the declaration names:
./scripts/pr_summary/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh contains some details about this script.

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No changes to technical debt.

You can run this locally as

./scripts/reporting/technical-debt-metrics.sh pr_summary

• The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
• The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).

[wwylele]

This is the big operator version of MvPolynomial.monomial_mul, but the direction is flipped. I understand this code is following the same direction as MvPolynomial.monomial_sum_one, so there is tension in existing lemmas which doesn't need to be resolved in the PR. I don't have strong opinion on this. Just calling it out in case someone else think strongly about it