[core] Fix false multiple decorator error when combining schema.output and tag

[ArnavBalyan]

Changes

• SchemaOutput inherits from tag and shares its lifecycle name, so multiplicity check tripped on the existing tag instance.
• Count only decorators of the same concrete class as self before raising, independent decorators sharing a lifecycle name now compose.

How I tested this

• UT

Notes

Checklist

• PR has an informative and human-readable title (this will be pulled into the release notes)
• Changes are limited to a single goal (no scope creep)
• Code passed the pre-commit check & code is left cleaner/nicer than when first encountered.
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future TODOs are captured in comments
• Project documentation has been updated if adding/changing functionality.