feat: add Function.prod and Function.diag

[linesthatinterlace]

This PR adds Function.prod and Function.diag and develops API for them and Pi.prod.

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[github-actions]

PR summary f51efbe0b8

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference
There are 6500 files with changed transitive imports taking up over 290232 characters: this is too many to display!
You can run ci-tools/scripts/pr_summary/import_trans_difference.sh all locally to see the whole output.

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Declarations diff

+ comp_prod_comp
+ const_prod
+ diag
+ diag_apply
+ diag_eq_iff
+ diag_prod_diag
+ exists_diag_apply_iff
+ fst_diag
+ injective_diag
+ leftInverse_uncurry_prod_prod_fst_comp_snd_comp
+ map_comp_diag
+ map_comp_prod
+ map_diag
+ prodMap
+ prodMap_eq_prod_map
+ prod_comp
+ prod_comp_prod
+ prod_ext
+ rightInverse_uncurry_prod_prod_fst_comp_snd_comp
+ snd_diag
++ eq_prod_iff_fst_comp_snd_comp
++ eq_prod_of_fst_comp_snd_comp
++ exists_fst_comp
++ exists_prod_apply_eq
++ exists_snd_comp
++ fst_comp_prod
++ fst_prod
++ prod_apply
++ prod_const_const
++ prod_eq_iff
++ prod_ext_iff
++ prod_fst_snd_comp
++ snd_comp_prod
++ snd_prod
+-+ prod
-++ prod_fst_snd
-++ prod_snd_fst

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.

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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).

[SnirBroshi]

This looks very cool!

[SnirBroshi]

Question:
I don't understand why we need both Pi.prod and Function.prod. Can't we have just the general version (Pi.prod)? (Related: #36902)
If the issue is dot notation, then it's worth mentioning that leanprover/lean4#1629 had some progress recently.

[eric-wieser]

This change is surely out of scope