[Merged by Bors] - feat(Algebra): add subsingleton of IsZero for AddCommGrpCat

[Thmoas-Guan]

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[github-actions]

✅ PR Title Formatted Correctly

The title of this PR has been updated to match our commit style conventions.
Thank you!

[github-actions]

PR summary 6a54a80825

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

++ isZero_iff_subsingleton
++ subsingleton_of_isZero

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 script/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/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).

[chrisflav]

Thanks!
maintainer delegate

[github-actions]

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

[jcommelin]

bors d+

[mathlib-bors]

✌️ Thmoas-Guan can now approve this pull request. To approve and merge a pull request, simply reply with bors r+. More detailed instructions are available here.

[Thmoas-Guan]

bors r+

[mathlib-bors]

Pull request successfully merged into master.

Build succeeded:

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