chore: split long file Mathlib.Data.Set.Basic

[kim-em]

No description provided.

[kim-em]

Will need a shake.

[github-actions]

PR summary 1ebb7babae

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference
There are 4968 files with changed transitive imports taking up over 213917 characters: this is too many to display!
You can run scripts/import_trans_difference.sh all locally to see the whole output.

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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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Decrease in tech debt: (relative, absolute) = (1.00, 0.03)

Current number	Change	Type
3158	-1	porting notes
34	-1	large files

Current commit 1ebb7babae
Reference commit fa9b36533f

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).

[Vierkantor]

I was hoping we could make some gains on the import structure: did you see a way to reduce the imports required for Data.Set.Basic, or is this pretty much the best we can do?

[kim-em]

I was hoping we could make some gains on the import structure: did you see a way to reduce the imports required for Data.Set.Basic, or is this pretty much the best we can do?

There's not much below Data.Set.Basic:

o.pdf

We could probably get GaloisConnections.Defs and Order.Monotone out of the way? Not sure how valuable that would be.