feat(Topology\Algebra\InfiniteSum): add limUnder_eq_tprod

[emlis42]

This PR adds limUnder_eq_tprod and limUnder_eq_tsum.

[github-actions]

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[github-actions]

PR summary 6d6d92b454

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

Declarations diff

+ HasProd.limUnder_eq
+ Multipliable.limUnder_eq_tprod

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.

---

No changes to strong technical debt.

No changes to weak technical debt.

[SnirBroshi]

Hello! Just wanted to mention that the slashes are backslashes (\) in this and some of your other PRs' titles, can you use slashes instead? (/)

[grunweg]

Hello from triage! Can you comment on whether you used AI for this project? Thanks!
(Per mathlib's AI policy, this is not forbidden in principle, but its usage must be disclosed.)