feat: add first-class Docker and Podman runtimes

[cofin]

Summary

• resolve Docker or Podman through one Docker-compatible API transport with explicit and automatic selection
• isolate managed containers by pytest session and serialize daemon-wide creation to fix concurrent port allocation races
• preserve Docker fixture aliases while adding runtime-neutral APIs, explicit stale cleanup, documentation, and required cross-runtime conformance

Clientless boundary

No Podman SDK or database service client is added. Runtime operations use the existing Docker-compatible API; representative provider validation uses the containerized service.

CI scope

This branch targets feat/provider-aware-ci. Runtime conformance is selected only for runtime/dependency changes, runs Docker and rootless Podman plus PostgreSQL and overlapping xdist session checks, and reports through CI required.

Validation

• uv run pre-commit run --all-files
• uv run mypy
• uv run pyright
• uv run slotscheck src/pytest_databases
• 30 focused runtime/ownership/host-port tests
• 4 real Docker conformance tests, including overlapping xdist controller teardown
• representative postgres_service smoke test
• make docs

Closes #146
Closes #152

[codecov-commenter]

Codecov Report

❌ Patch coverage is 45.82043% with 175 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (feat/provider-aware-ci@51a063d). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/pytest_databases/runtime.py	47.36%	87 Missing and 13 partials ⚠️
src/pytest_databases/_service.py	46.77%	63 Missing and 3 partials ⚠️
src/pytest_databases/__init__.py	0.00%	3 Missing ⚠️
src/pytest_databases/docker/yugabyte.py	0.00%	3 Missing ⚠️
src/pytest_databases/docker/minio.py	0.00%	1 Missing ⚠️
src/pytest_databases/docker/rustfs.py	0.00%	1 Missing ⚠️
src/pytest_databases/docker/spanner.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@                    Coverage Diff                    @@
##             feat/provider-aware-ci     #154   +/-   ##
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  Coverage                          ?   11.95%           
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  Files                             ?       24           
  Lines                             ?     2082           
  Branches                          ?      169           
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  Hits                              ?      249           
  Misses                            ?     1798           
  Partials                          ?       35           

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