feat(RingTheory/Bialgebra): expose (Add)MonoidAlgebra.liftMulEquiv

[kim-em]

This PR marks MonoidAlgebra.liftMulEquiv and AddMonoidAlgebra.liftMulEquiv
@[expose, simps!], matching mapDomainBialgHomMulEquiv in the same file, which
is built the same way out of an equivalence composed with WithConv.equiv and
already carries both attributes. Without them the definitions are opaque
downstream: their bodies cannot be unfolded, and no lemma computes their
application or the application of their inverse, so liftMulEquiv cannot be
related to lift outside this file.

🤖 Prepared with Claude Code

[github-actions]

PR summary 0a14478001

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

Declarations diff (regex)

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

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 0a14478).

• +4 new declarations
• −0 removed declarations

+AddMonoidAlgebra.liftMulEquiv_apply_ofConv_apply
+AddMonoidAlgebra.liftMulEquiv_symm_apply_apply
+MonoidAlgebra.liftMulEquiv_apply_ofConv_apply
+MonoidAlgebra.liftMulEquiv_symm_apply_apply

---

No changes to strong technical debt.

No changes to weak technical debt.

Current commit 0a14478001
Reference commit caa4dbde35

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).