feat(Algebra): define `PrimitiveIdempotents`

[Whysoserioushah]

Co-authored-by : @jjaassoonn

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[github-actions[bot]]

PR summary 63dcdd9437

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference
Mathlib.Algebra.DirectSum.Idempotents (new file)	1092

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Declarations diff

+ completeOrthogonalIdempotents_idempotent + decompose_eq_mul_idempotent + idempotent + isIdempotentElem_idempotent

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).

[erdOne]

And I think (also judging from the "large-import" tag) this belongs to Mathlib.Algebra.DirectSum.Idempotents or something similar.

Also please update the PR title so that it matches with the content.

[kbuzzard]

Thanks a lot!

bors d+

[mathlib-bors[bot]]

:v: Whysoserioushah can now approve this pull request. To approve and merge a pull request, simply reply with bors r+. More detailed instructions are available here.

[Whysoserioushah]

bors r+

[mathlib-bors[bot]]

Pull request successfully merged into master.

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