feat(Probability): proper kernels

[YaelDillies]

Define proper kernels, which are self-kernels which can meaningfully be restricted to an event.

From GibbsMeasure

Co-authored-by: Kalle Kytölä
Co-authored-by: Kin Yau James Wong

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[github-actions]

PR summary ca69cdd5c6

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference
Mathlib.Probability.Kernel.Proper (new file)	1344

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Declarations diff

+ IsProper
+ IsProper.inter_eq_indicator_mul
+ IsProper.lintegral_mul
+ IsProper.of_inter_eq_indicator_mul
+ IsProper.of_restrict_eq_indicator_smul
+ IsProper.restrict_eq_indicator_smul
+ IsProper.setLIntegral_eq_bind
+ IsProper.setLIntegral_eq_indicator_mul_lintegral
+ IsProper.setLIntegral_inter_eq_indicator_mul_setLIntegral
+ isProper_iff_inter_eq_indicator_mul
+ isProper_iff_restrict_eq_indicator_smul

You can run this locally as follows

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

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

The doc-module for script/declarations_diff.sh contains some details about this script.

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No changes to technical debt.

You can run this locally as

./scripts/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).