refactor(MeasureTheory): golf Mathlib/MeasureTheory/Function/SimpleFunc

[yuanyi-350]

• rewrites Measurable.add_simpleFunc and Measurable.simpleFunc_add in MeasureTheory/Function/SimpleFunc to use SimpleFunc.measurable_bind instead of explicit inductions together with manual piecewise/support arguments

Extracted from #38104, migrate from #38107

[yuanyi-350]

!bench

[leanprover-radar]

Benchmark results for fbcd08b against 9268b22 are in. No significant results found. @yuanyi-350

• 🟥 build//instructions: +6.3G (+0.00%)

Small changes (1🟥)

• 🟥 build/module/Mathlib.MeasureTheory.MeasurableSpace.Card//instructions: +407.0M (+3.39%)

[github-actions]

PR summary 9268b22206

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).

[yuanyi-350]

I ran a profiler comparison for the changed declarations in this PR.

Results (seconds):

• Measurable.add_simpleFunc: 0.140375 -> 0.019971 (-85.77%)
• Measurable.simpleFunc_add: 0.136454 -> 0.018850 (-86.19%)

Overall:

• both rewritten proofs are substantially faster than the previous induction-based versions.

[grunweg]

Seems sensible to me, thanks! Let's have another pair of eyes to double-check that we don't want to keep the old proofs for some reason:
maintainer merge

[github-actions]

🚀 Pull request has been placed on the maintainer queue by grunweg.