test(marketplace): cover registered ref install flow

[abhinavgautam01]

Description

Adds integration-tier coverage for marketplace registered --ref propagation through the full install path.

This covers the follow-up from #1918 by exercising apm install plugin@marketplace through marketplace resolution, dependency parsing, manifest persistence, lockfile writing and the downloader boundary. The test verifies both GitHub-family and GitLab marketplace flows, including the structured GitLab git + path dependency shape.

Fixes #1918

Type of change

• Bug fix
• New feature
• Documentation
• Maintenance / refactor

Testing

• Tested locally
• All existing tests pass
• Added tests for new functionality (if applicable)

Validation run:

uv run --extra dev ruff format --check src/ tests/
uv run --extra dev ruff check tests/integration/test_marketplace_ref_install_e2e.py
uv run --extra dev pytest tests/integration/test_marketplace_ref_install_e2e.py tests/unit/marketplace/
test_marketplace_resolver.py::TestMarketplaceRegisteredRefPropagation -q
git diff --check

Results:

• Ruff format check passed
• Ruff lint passed
• Focused pytest passed: 9 passed
• Diff check passed

Spec conformance (OpenAPM v0.1)

If this PR changes behaviour that an OpenAPM v0.1 req-XXX covers,
confirm the three-step ritual (see CONTRIBUTING.md "Adding or
changing a normative requirement"):

• Spec edit: docs/src/content/docs/specs/openapm-v0.1.md updated
  (new/changed anchor + prose + Appendix C
  row).

• Manifest edit: docs/src/content/docs/specs/manifests/openapm-v0.1.requirements.yml
  updated.

• Test edit: a @pytest.mark.req("req-XXX") test under
  tests/spec_conformance/ added or extended.

• CONFORMANCE.{md,json} regenerated via
  uv run --extra dev python -m tests.spec_conformance.gen_statement
  and committed.

• N/A -- this PR does not change OpenAPM-observable behaviour.

[Copilot]

Pull request overview

Adds a new integration-tier test that exercises the end-to-end apm install <plugin>@<marketplace> flow to ensure a registered marketplace --ref is propagated all the way through resolution, persistence (apm.yml / lockfile), and into the downloader boundary for both GitHub-family and GitLab marketplaces.

Changes:

• Introduces a hermetic integration test that stubs only external I/O seams (marketplace fetch/cache, existence probe, downloader) while running the rest of the install pipeline on production code.
• Verifies --ref propagation for both dependency persistence formats:
  • GitHub-family string dependency form
  • GitLab structured {git, path, ref} dependency form
• Asserts clone URL components via urllib.parse.urlparse (component-level checks rather than substring assertions).