feat(Algebra/CategoryTheory): Add CommAlgebraCat

[javierlcontreras]

---

• depends on: [Merged by Bors] - refactor(Algebra/Category): turn homs in AlgebraCat into a structure #19065

[github-actions]

PR summary 0aa334030b

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

Declarations diff

+ CommAlgebra
+ CommAlgebraCat
+ coe_of
+ instance : Category (CommAlgebraCat R) := by unfold
+ instance : CoeSort (CommAlgebraCat R) (Type v) where coe A := A.obj.carrier
+ isComm
+ of

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.

---

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).

[YaelDillies]

I would suggest you inline this

[YaelDillies]

Suggested change

	def CommAlgebraCat := FullSubcategory (fun (A : AlgebraCat R) => isComm A)
	def CommAlgebraCat := FullSubcategory fun A : AlgebraCat R ↦ ∀ a b : A, a * b = b * a

[mathlib4-dependent-issues-bot]

This PR/issue depends on:

• [Merged by Bors] - refactor(Algebra/Category): turn homs in AlgebraCat into a structure #19065
  By Dependent Issues (🤖). Happy coding!