feat(CategoryTheory): split up a product into a binary product

[dagurtomas]

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This is used in #18497 to prove that light condensed modules satisfy countable AB4*

[github-actions]

PR summary 6326a1a718

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference
Mathlib.CategoryTheory.Limits.Shapes.PiProd	405

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Declarations diff

+ Pi.binaryFanOfProp
+ Pi.binaryFanOfPropIsLimit
+ Pi.map_eq_prod_map
+ hasBinaryProduct_of_products

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).