feat(Algebra/Ring): introduce pullback for RingHom and AlgHom

[BryceT233]

This PR introduces pullback for RingHom and AlgHom and adds IsLocalHom, IsLocalRing instances related to them.

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[github-actions]

PR summary 5fdfe6a214

Import changes for modified files

Dependency changes

File	Base Count	Head Count	Change
Mathlib.RingTheory.LocalRing.LocalSubring	1265	1266	+1 (+0.08%)

Import changes for all files

Files	Import difference
Mathlib.RingTheory.LocalRing.LocalSubring	1

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Declarations diff

+ isLocalHom_eqLocus_subtype
+ isLocalRing_algHomPullback
+ isLocalRing_eqLocus
+ isLocalRing_ringHomPullback
+ isUnit_eqLocus_mk_iff
++ isLocalHom_pullbackFst
++ isLocalHom_pullbackSnd
++ isUnit_pullback_mk_iff
++ pullback
++ pullbackFst
++ pullbackSnd
++ surjective_pullbackFst_of_surjective
++ surjective_pullbackSnd_of_surjective

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).