chore: make RingHom.id implicit-reducible

[sgouezel]

This has no bad performance impact, and is in line with the reducibility change made in #38315. Discussion at #mathlib4 > backward.isDefEq.respectTransparency: bundled homomorphisms @ 💬

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[mathlib-bors]

This pull request is now in draft mode. No active bors state needed cleanup.

While this PR remains draft, bors will ignore commands on this PR. Mark it ready for review before using commands like bors r+ or bors try.

[sgouezel]

!radar

[leanprover-radar]

Benchmark results for eb85ab0 against a78e049 are in. No significant results found. @sgouezel

• ✅ build//instructions: -9.5G (-0.01%)

Small changes (2🟥)

• 🟥 build/module/Mathlib.Algebra.Module.ZLattice.Basic//instructions: +3.7G (+4.12%)
• 🟥 build/module/Mathlib.Tactic.Attr.Core//instructions: +377.9M (+15.62%)

[github-actions]

PR summary a78e049222

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

Declarations diff

No declarations were harmed in the making of this PR! 🐙

You can run this locally as follows

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

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

The doc-module for scripts/pr_summary/declarations_diff.sh 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).

[sgouezel]

!radar

[leanprover-radar]

Benchmark results for dd7df5e against a78e049 are in. No significant results found. @sgouezel

• ✅ build//instructions: -19.1G (-0.01%)

Medium changes (1🟥)

• 🟥 build/module/Mathlib.RepresentationTheory.Coinvariants//instructions: +9.7G (+12.69%)

Small changes (1✅, 2🟥)

• 🟥 build/module/Mathlib.Algebra.Module.ZLattice.Basic//instructions: +3.7G (+4.08%)
• ✅ build/module/Mathlib.SetTheory.Cardinal.Free//instructions: -514.3M (-5.57%)
• 🟥 build/module/Mathlib.Tactic.Attr.Core//instructions: +382.3M (+15.80%)