feat(CategoryTheory/Shift): lifting of single functors

[joelriou]

Let C, D and E be categories. Let A be an additive monoid. Assume that D and E have shifts by A and that we have a fully faithful functor G : D ⥤ A which commutes with shifts. Given F : SingleFunctors C E A, and a family of functors Φ a : C ⥤ D with isomorphisms Φ a ⋙ G ≅ F.functor a for all a : A, we lift F in SingleFunctor C D A.

---

[github-actions]

PR summary b6a5119897

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference
Mathlib.CategoryTheory.Shift.SingleFunctorsLift (new file)	708

---

Declarations diff

+ additive_iff_of_iso
+ commShiftIso_hom_inv_id_apply
+ commShiftIso_inv_hom_id_apply
+ instance [Preadditive C] [Preadditive D] [Preadditive E] [G.Additive] (a : A)
+ lift
+ liftPostcompIso
+ map_lift_shiftIso_hom_app
+ map_shiftIso_hom_app
+ shiftIso

You can run this locally as follows

## from your `mathlib4` directory:
git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci

## summary with just the declaration names:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh <optional_commit>

## more verbose report:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh in the mathlib-ci repository contains some details about this script.

---

No changes to technical debt.

This script lives in the mathlib-ci repository. To run it locally, from your mathlib4 directory:

git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci
../mathlib-ci/scripts/reporting/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).