feat(CategoryTheory/Triangulated): abelian subcategories

[joelriou]

This PR adds a criteria to show that an additive subcategory of a triangulated category is abelian. (This shall be used to show that the heart of a t-structure is an abelian category.)

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• depends on: feat(CategoryTheory): constructor for abelian categories #35381

[github-actions]

PR summary 99884c2730

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference
Mathlib.CategoryTheory.Triangulated.TStructure.AbelianSubcategory (new file)	1107

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Declarations diff

+ abelian
+ admissibleMorphism
+ epi_πQ
+ exists_desc_πQ
+ exists_distinguished_triangle_of_epi
+ exists_lift_ιK
+ hasCokernel
+ hasCokernel_of_admissibleMorphism
+ hasKernel
+ hasKernel_of_admissibleMorphism
+ isColimitCokernelCofork
+ isColimitCokernelCoforkOfDistTriang
+ isLimitKernelFork
+ isLimitKernelForkOfDistTriang
+ mk'
+ mono_ιK
+ mor₁_πQ
+ shift_ι_map_ιK
+ vanishing_from_positive_shift
+ ιK
+ ιK_mor₁
+ ι_map_πQ
+ πQ

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 scripts/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).

[mathlib-dependent-issues]

This PR/issue depends on:

• feat(CategoryTheory): constructor for abelian categories #35381
  By Dependent Issues (🤖). Happy coding!