[WIP] Improve stability of cpython.gc.uncollectable_objects metric

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Original prompt

Metric cpython.gc.uncollectable_objects counter, {object}
- [improvement] Metric 'cpython.gc.uncollectable_objects' is not stable; stability = development.
Data point 0
- [violation] Required attribute 'cpython.gc.generation' is not present.
generation = 0
- [violation] Attribute 'generation' does not exist in the registry.
- [improvement] Attribute name 'generation' must include a namespace (e.g. '{namespace}.{attribute_key}')
Data point 0
- [violation] Required attribute 'cpython.gc.generation' is not present.
generation = 1
- [violation] Attribute 'generation' does not exist in the registry.
- [improvement] Attribute name 'generation' must include a namespace (e.g. '{namespace}.{attribute_key}')
Data point 0
- [violation] Required attribute 'cpython.gc.generation' is not present.
generation = 2
- [violation] Attribute 'generation' does not exist in the registry.
- [improvement] Attribute name 'generation' must include a namespace (e.g. '{namespace}.{attribute_key}')

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