feat: semidirect product of Lie algebras - adding simp lemmas for toProd.symm and toProdl.symm

[Ljon4ik4]

As an R-module the semidirect product of two Lie algebras K ⋊⁅ψ⁆ L is isomorphic to K × L.
The simp lemmas for the reverse direction of this isomorphisms were missing and are added in this PR.

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[github-actions]

PR summary 994f38f1e6

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)

+ toProd_symm_apply
+ toProdl_symm_coe

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 994f38f).

• +2 new declarations
• −0 removed declarations

+LieAlgebra.SemiDirectSum.toProd_symm_apply
+LieAlgebra.SemiDirectSum.toProdl_symm_coe

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No changes to strong technical debt.

No changes to weak technical debt.

Current commit 994f38f1e6
Reference commit fd1d54bcac

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).

[github-actions]

✅ PR Title Formatted Correctly

The title of this PR has been updated to match our commit style conventions.
Thank you!