[Merged by Bors] - chore(SimpleGraph/Extremal): update IsExtremal docstrings

[mitchell-horner]

Update docstrings for IsExtremal to clarify definition.

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See #28719 (comment).

The docstring left out the fact that the maximum is taken on simple graphs with fixed vertices. This is implicit in the definition of SimpleGraph. The docstring now explicitly notes this to avoid confusion and align with the definition you might read in a textbook somewhere.

[github-actions]

PR summary ec382b5a79

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).

[vihdzp]

Thanks!

[b-mehta]

Thanks!

bors merge

[mathlib-bors]

Pull request successfully merged into master.

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