refactor(Topology/Compactness): deduce nhdsSet_prod_eq_biSup from the inf version

[FrankieNC]

Answer the TODO above IsCompact.nhdsSet_inf_eq_biSup: prove IsCompact.mem_nhdsSet_inf_of_forall directly by compact induction and deduce the product version from it, instead of the other way around. The deduction endows Y with the indiscrete topology, so that 𝓝ˢ K ×ˢ l becomes 𝓝ˢ (K ×ˢ {y₀}) ⊓ comap Prod.snd l with K ×ˢ {y₀} compact.

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[github-actions]

PR summary ebbf8e4398

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Declarations diff (regex)

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You can run this locally as follows

## from your `mathlib4` directory:
git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci

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

## more verbose report:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh in the mathlib-ci repository contains some details about this script.

Declarations diff (Lean)

✅ Lean-aware diff — post-build, computed from the Lean environment (commit ebbf8e4).

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• −0 removed declarations

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No changes to strong technical debt.

No changes to weak technical debt.

Current commit ebbf8e4398
Reference commit e13dd6052c

This script lives in the mathlib-ci repository. To run it locally, from your mathlib4 directory:

git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci
../mathlib-ci/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).

[mathlib-merge-conflicts]

This pull request has conflicts, please merge master and resolve them.