feat(Algebra): add zpow_right_injective

[lman310]

Add zpow_right_injective, stating that for a nontrivial element a of a
multiplicatively torsion free group, the map n : ℤ ↦ a ^ n is injective,
as well as the corresponding additive theorem zsmul_left_injective using
to_additive

Use the new additive theorem in CharZero.of_isAddTorsionFree, replacing its
dependency on the general smul_left_injective. This allows
CharZero.of_isAddTorsionFree to move from
Mathlib.Algebra.Module.Torsion.Free to the earlier
Mathlib.Algebra.Module.NatInt, resolving the existing TODO

Codex was used to find the appropriate file Mathlib.Algebra.Module.NatInt for moving CharZero.of_isAddTorsionFree

[github-actions]

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[github-actions]

PR summary e0b2beb1d5

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

---

Declarations diff (regex)

+ zpow_right_injective

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 e0b2beb).

• +2 new declarations
• −0 removed declarations

+zpow_right_injective
+zsmul_left_injective

---

No changes to strong technical debt.

No changes to weak technical debt.

Current commit e0b2beb1d5
Reference commit 19996d632e

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).

[felixpernegger]

awaiting-author

[felixpernegger]

@lman310 can you try to merge master and see if that fixes the ci issue

[lman310]

-awaiting-author