feat(Torsion/Basic): Add a few convenient lemmas for torsion submodules

[xgenereux]

This PR adds a few convenient lemmas in Torsion/Basic.

In particular, it adds:

• A version of torsionBySet_span_singleton_eq for Ideals. These two are added to the simp set.
• Show two instances of isTorsionBy/isTorsionBySet being IsTorsion in the form of torsionBy_isTorsion_nonZeroDivisor and torsionBySet_ideal_isTorsion_of_noZeroDivisors.
• Add a version of iSup_torsionBySet_ideal_eq_torsionBySet_iInf and supIndep_torsionBySet_ideal for sup instead of iSup.

Note: To go from iSup to sup I need to talk about Fin 2 which requires Finset.univ_fin2 that is in Mathlib but in a weird place. I just put it as a have in my proof.

Note2: one could also use {P,Q} and id instead of the map from Fin 2 but that makes the proof of disjoint_torsionBySet_ideal inconvenient.

Co-authored-by: María Inés de Frutos Fernández <mariaines.dff@gmail.com>

---

[github-actions]

PR summary af97ef4b5b

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

Declarations diff

+ disjoint_torsionBySet_ideal
+ sup_torsionBySet_ideal_eq_torsionBySet_inf
+ torsionBySet_ideal_isTorsion_of_noZeroDivisors
+ torsionBySet_ideal_span_singleton_eq
+ torsionBy_isTorsion_nonZeroDivisor

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 scripts/declarations_diff.sh contains some details about this script.

---

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).