feat(Data/Fintype/Card): existsUnique_notMem_image_of_injective_of_card_succ

[cjrl]

This pull requests adds a small theorem existsUnique_notMem_image_of_injective_of_card_succ to Mathlib/Data/Fintype/Card that says given an injective map f : α → β such that β has cardinality one more than α, there exists a unique element of β not in the image of f.

This can be viewed as going in the opposite direction of card_lt_of_injective_of_notMem.

This little fact is needed for our Latin Square PR #36698.

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[github-actions]

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[github-actions]

PR summary 322515540d

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

+ existsUnique_notMem_image_of_injective_of_card_succ

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).

[cjrl]

+t-set-theory