chore(Data/PFunctor): fix defeq abuse in PFunctor.Obj

[plp127]

Fix defeq abuse with PFunctor.Obj by using explicit constructors and destructors.

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[github-actions]

PR summary 5c64610700

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

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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

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 5c64610).

• +10 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

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Decrease in strong tech debt: (relative, absolute) = (12.00, 0.00)

Current number	Change	Type (strong)
backward.isDefEq.respectTransparency	4915	-12

No changes to weak technical debt.

Current commit 5c64610700
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).