feat: klDiv and scalar multiplication

[RemyDegenne]

The Kullback-Leibler divergence in Mathlib is defined for finite measures, not just probability measures. This PR adds lemmas that show how klDiv changes when we multiply one or both of the measures by a scalar.

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[github-actions]

PR summary 738faa5527

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

+ AbsolutelyContinuous.smul_right
+ coe_nnreal_smul
+ klDiv_ne_top
+ klDiv_smul_both
+ klDiv_smul_right_eq_smul_left
+ llr_smul_both
+ llr_smul_inv_left_eq_smul_right
+ llr_smul_nnreal_both
+ llr_smul_nnreal_left
+ llr_smul_nnreal_right
+ rnDeriv_smul_both
+ toReal_klDiv_smul_both
+ toReal_klDiv_smul_left
+ toReal_klDiv_smul_right
+ toReal_klDiv_smul_right_eq_smul_left

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 scripts/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).