feat(Algebra/Group/Even): Clean up file, add Aesop automation

[artie2000]

• Rename some theorems for consistency and to remove some primed variants
• Make API for IsSquare / Even consistent between the "official" definition and equivalent ones
• Add and correct simp and aesop attributes to enable sensible automation
• Add test examples for concluding IsSquare / Even by aesop

Moves:
Even.nsmul' -> Even.even_nsmul
Even.zsmul' -> Even.even_zsmul
isSquare_zero -> IsSquare.zero

Deletions:
isSquare_of_exists_sq (prefer IsSquare.sq)

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[github-actions]

PR summary 9d5d902e9c

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

+ Even.nsmul'
+ Even.zsmul'
+ IsSquare.zero
+ _
+ exists_apply_eq_and_isSquare
+ isSquare_iff_exists_mul_self
- even_add_self
- isSquare_of_exists_sq

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).

[YaelDillies]

Could you write a library note explaining the priority you choose here?

[artie2000]

I'll do this in general in #20477 and then review the priorities in this PR.