feat(Order/Directed): DirectedOn and products

[mans0954]

A couple of results about DirectedOn and Pi products:

• When a set of cross sections is DirectedOn, then the projection onto a fibre is DirectedOn
• For each element i in the base space, let d i be a subset of the fibre at i. Then the product of the d i is DirectedOn.

We also give pairwise product versions of these results.

Inspired by #15412

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[github-actions]

PR summary e1f50f43f5

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

+ fst
+ proj
+ snd
++ prodMk

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).