Preserve marketplace plugin package metadata

[huanghuoguoguo]

Summary

Preserve package metadata when installing marketplace plugin packages:

• carry the inspected package author/name/version through marketplace package task metadata
• avoid re-transferring locally available marketplace package archives
• cover package metadata extraction in connector unit tests

Validation

• uv run --python 3.12 pytest tests/unit_tests/plugin/test_connector_pure.py -q

[codecov]

Codecov Report

❌ Patch coverage is 16.66667% with 15 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/langbot/pkg/plugin/connector.py	16.66%	15 Missing ⚠️

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