chore(Data/PFunctor): reduce defeq abuse around PFunctor.W

[plp127]

Reduce the defeq abuse around PFunctor.W by adding some API.

---

• depends on: chore(Data/PFunctor): fix defeq abuse in PFunctor.Obj #43056

[github-actions]

PR summary c01493b5bf

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

Declarations diff (regex)

+ Comp.mk_run
+ Comp.run_mk
+ Obj.eta
+ Obj.fst
+ Obj.fst_mk
+ Obj.mk
+ Obj.rec
+ Obj.rec_mk
+ Obj.snd
+ Obj.snd_mk
+ W.casesOn
+ W.children_mk
+ W.fst_dest
+ W.head_mk
+ W.induction
+ W.rec
+ W.rec_mk
+ W.rec_uniq
+ W.snd_dest

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.

Declarations diff (Lean)

✅ Lean-aware diff — post-build, computed from the Lean environment (commit c01493b).

• +19 new declarations
• −0 removed declarations

+Functor.Comp.mk_run
+Functor.Comp.run_mk
+PFunctor.Obj.eta
+PFunctor.Obj.fst
+PFunctor.Obj.fst_mk
+PFunctor.Obj.mk
+PFunctor.Obj.rec
+PFunctor.Obj.rec_mk
+PFunctor.Obj.snd
+PFunctor.Obj.snd_mk
+PFunctor.W.casesOn
+PFunctor.W.children_mk
+PFunctor.W.fst_dest
+PFunctor.W.head_mk
+PFunctor.W.induction
+PFunctor.W.rec
+PFunctor.W.rec_mk
+PFunctor.W.rec_uniq
+PFunctor.W.snd_dest

---

Decrease in strong tech debt: (relative, absolute) = (14.00, 0.00)

Current number	Change	Type (strong)
backward.isDefEq.respectTransparency	4913	-14

No changes to weak technical debt.

Current commit c01493b5bf
Reference commit b63493a474

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.py 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:

• chore(Data/PFunctor): fix defeq abuse in PFunctor.Obj #43056
  By Dependent Issues (🤖). Happy coding!