feat(Mathlib/Data): setOf_eq_singleton_iff_of_nodup

[LeoDog896]

Adds setOf_eq_singleton_iff_of_nodup with the generalizing setOf_nodup_perm.

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[github-actions]

PR summary 2c1b10e739

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

+ List.setOf_fintype
+ setOf_eq_singleton_iff_of_nodup
+ setOf_inj
+ setOf_mem_empty
+ setOf_mem_eq_empty_iff
+ setOf_nodup_perm

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).

[LeoDog896]

Note that setOf_mem_empty, setOf_mem_eq_empty_iff, and setOf_inj are no longer used in this PR. They still seem like useful lemmas to keep, but I can split them to a separate PR / delete them if needed.