Add DB client metrics to aiopg instrumentation

[henry3260]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Adds DB client operation duration and returned rows metrics to aiopg when database semantic-convention opt-in is enabled. It preserves the existing async execution path and supports optional meter providers for automatic and manual instrumentation. No additional dependencies are required.

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• uv run --all-packages --group dev tox -e py312-test-instrumentation-aiopg-wrapt2
• uv run --all-packages --group dev pre-commit run ruff --all-files

Does This PR Require a Core Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated