feat(Algebra/Group/Commutator): tag addCommutatorElement as a scoped instance

[SnirBroshi]

#34784 additivized commutators and made the multiplicative commutator instance available under open scoped commutatorElement.
This makes the additive instance available under open scoped addCommutatorElement.

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Should we instead make it scoped under the addCommutatorElement namespace?
The existing usages of additive commutators come from decls marked with open scoped commutatorElement in @[to_additive], and to_additive seemingly doesn't mind that the additivized version is not an instance. So I think they don't have to live in the same namespace.

[github-actions]

PR summary cc26c21489

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

No declarations were harmed in the making of this PR! 🐙

You can run this locally as follows

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

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

The doc-module for scripts/pr_summary/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/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).

[tb65536]

I think it should probably be a different namespace, because otherwise open scoped commutatorElement would lead to the same notation being used for two different definitions.

[SnirBroshi]

Done, although I think it's very rare to have both Group and AddGroup at the same time (Ring gives GroupWithZero and not Group).

[tb65536]

Yeah, I know, it just seemed better hygienically to avoid activating them at the same time.

[tb65536]

Thanks!

maintainer merge

[github-actions]

🚀 Pull request has been placed on the maintainer queue by tb65536.