chore: rename DivInvMonoid.Pow

[eric-wieser]

This didn't match the naming convention at all.

Loogle tells me that ZPow is slightly more common than PowInt, though both are used.

This is an instance, so the name needs no deprecation

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[github-actions]

PR summary e3ac7530ba

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

+ DivInvMonoid.toZPow
+ SubNegMonoid.toZSMul
- DivInvMonoid.Pow
- SubNegMonoid.SMulInt

You can run this locally as follows

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

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

The doc-module for script/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/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).