refactor: golf Function/SimpleFunc, Function/LpSeminorm, Constructions/Polish

[yuanyi-350]

This PR is derived from #38104.

Originally this was intended as a selective port for:

• Mathlib/MeasureTheory/Function/SimpleFunc.lean
• Mathlib/MeasureTheory/Function/LpSeminorm/Basic.lean
• Mathlib/MeasureTheory/Constructions/Polish/Basic.lean

Per the latest instruction, this branch is opened directly from the source PR head instead of rebuilding a reduced-history selective branch in a separate worktree.

As a result, the branch may still contain the broader source PR diff, not just the three files above.

Compile checks were intentionally skipped for this port.

[github-actions]

PR summary 8e3c989104

Import changes for modified files

Dependency changes

File	Base Count	Head Count	Change
Mathlib.MeasureTheory.Function.ConditionalExpectation.Real	2324	2340	+16 (+0.69%)
Mathlib.Probability.ProductMeasure	2423	2438	+15 (+0.62%)

Import changes for all files

Files	Import difference
15 files Mathlib.Probability.Combinatorics.BinomialRandomGraph.Defs Mathlib.Probability.Distributions.Binomial Mathlib.Probability.Distributions.SetBernoulli Mathlib.Probability.HasLawExists Mathlib.Probability.IdentDistribIndep Mathlib.Probability.Independence.Conditional Mathlib.Probability.Independence.InfinitePi Mathlib.Probability.Independence.ZeroOne Mathlib.Probability.Kernel.CondDistrib Mathlib.Probability.Kernel.Condexp Mathlib.Probability.Kernel.Disintegration.Integral Mathlib.Probability.Kernel.Disintegration.Unique Mathlib.Probability.Kernel.IonescuTulcea.Traj Mathlib.Probability.Moments.SubGaussian Mathlib.Probability.ProductMeasure	15
23 files Mathlib.MeasureTheory.Function.ConditionalExpectation.Real Mathlib.MeasureTheory.Function.FactorsThrough Mathlib.Probability.BorelCantelli Mathlib.Probability.Kernel.CompProdEqIff Mathlib.Probability.Kernel.Composition.AbsolutelyContinuous Mathlib.Probability.Kernel.Disintegration.Density Mathlib.Probability.Kernel.Disintegration.StandardBorel Mathlib.Probability.Kernel.Posterior Mathlib.Probability.Kernel.RadonNikodym Mathlib.Probability.Martingale.Basic Mathlib.Probability.Martingale.BorelCantelli Mathlib.Probability.Martingale.Centering Mathlib.Probability.Martingale.Convergence Mathlib.Probability.Martingale.OptionalSampling Mathlib.Probability.Martingale.OptionalStopping Mathlib.Probability.Martingale.Upcrossing Mathlib.Probability.Process.Adapted Mathlib.Probability.Process.Filtration Mathlib.Probability.Process.HittingTime Mathlib.Probability.Process.LocalProperty Mathlib.Probability.Process.PartitionFiltration Mathlib.Probability.Process.Predictable Mathlib.Probability.Process.Stopping	16

---

Declarations diff

+ instSemilatticeInf
+ instSemilatticeSup

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.

You can run this locally as

./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).