refactor(AlgebraicGeometry/Sites/Small): golf and remove defeqs

[tb65536]

This PR golfs and removes some defeqs. Some proofs with the help of Claude, with further golfing by myself.

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[github-actions]

PR summary e7c604fc6a

Import changes for modified files

Dependency changes

File	Base Count	Head Count	Change
Mathlib.AlgebraicGeometry.Sites.Small	2349	2350	+1 (+0.04%)

Import changes for all files

Files	Import difference
5 files Mathlib.AlgebraicGeometry.Sites.AffineEtale Mathlib.AlgebraicGeometry.Sites.Affine Mathlib.AlgebraicGeometry.Sites.EtalePoint Mathlib.AlgebraicGeometry.Sites.Etale Mathlib.AlgebraicGeometry.Sites.Small	1

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Declarations diff (regex)

+ Precoverage.over
+ map_functorPullback_mem_coverings

You can run this locally as follows

## from your `mathlib4` directory:
git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci

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

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

The doc-module for scripts/pr_summary/declarations_diff.sh in the mathlib-ci repository contains some details about this script.

Declarations diff (Lean)

✅ Lean-aware diff — post-build, computed from the Lean environment (commit e7c604f).

• +1 new declarations
• −1 removed declarations

-AlgebraicGeometry.Scheme.smallPretopology.congr_simp
+CategoryTheory.Precoverage.over

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Decrease in strong tech debt: (relative, absolute) = (3.00, 0.00)

Current number	Change	Type (strong)
5622	-3	backward.isDefEq.respectTransparency

No changes to weak technical debt.

Current commit e7c604fc6a
Reference commit e469acc1a6

This script lives in the mathlib-ci repository. To run it locally, from your mathlib4 directory:

git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci
../mathlib-ci/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).