[Merged by Bors] - perf: speedup using Submodule.restrictScalars_mem instead of relying on defeq

[alreadydone]

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[alreadydone]

!bench

[github-actions]

PR summary 407b6bffc3

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

No declarations were harmed in the making of this PR! 🐙

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).

[leanprover-bot]

Here are the benchmark results for commit 407b6bf.
There were significant changes against commit da9df8d:

  Benchmark                             Metric         Change
  ===========================================================
+ ~Mathlib.RingTheory.Ideal.Cotangent   instructions   -21.6%
+ ~Mathlib.RingTheory.Kaehler.Basic     instructions    -6.2%

[alreadydone]

These two occurences were discovered because they timed out in another PR; maybe more are still hidden. Not sure who might know about more situations that could benefit from this. Maybe @erdOne?

[erdOne]

I feel like this defeq abuse(?) happen very often (and I'm definitely guilty of many of them) that I unfortunately cannot give you a list of where it occurs.

[riccardobrasca]

This looks like a positive change, thanks!

bors merge

[mathlib-bors]

Pull request successfully merged into master.

Build succeeded:

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