fix(sessions): honor Windows sqlite session URIs

[sbguangha]

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Link to Issue or Description of Change

1. Link to an existing issue (if applicable):

• N/A (found while running the documented unit tests on Windows)

2. Or, if no issue exists, describe the change:

Problem:
On Windows, SqliteSessionService and the CLI sqlite:// factory do not treat drive-letter session URIs the way file:// artifact URIs already do.

urlparse("sqlite:///C:/tmp/adk%20sessions.db").path stays '/C:/tmp/adk%20sessions.db' (percent-encoding is not decoded by urlparse). The factory only stripped a leading /, so --session_service_uri created a database whose filename still contained literal %20. The same helper also rejected the documented SQLAlchemy Windows form when the official unit test built sqlite+aiosqlite://// + C:\... (lstrip('/') does nothing on a drive path), so test_sqlite_session_service_accepts_absolute_sqlite_urls failed on Windows.

Steps to Reproduce:

1. On Windows, uv venv --python 3.11 .venv and uv sync.
2. pytest tests/unittests/sessions/test_session_service.py::test_sqlite_session_service_accepts_absolute_sqlite_urls.
3. Or pass --session_service_uri sqlite:///C:/Users/Someone/My%20Docs/sessions.db to adk web.

Expected Behavior:
sqlite:///C:/path/to.db (and a percent-encoded space) opens that filesystem path, matching SQLAlchemy and the existing file:// artifact factory.

Observed Behavior:
The absolute-URL unit test fails because the constructed URI is not a valid Windows sqlite URL. A percent-encoded CLI URI creates adk%20sessions.db instead of adk sessions.db.

Environment Details:

• ADK checkout: main @ 7b246e0
• Desktop OS: Windows 10
• Python Version: 3.11.15

Solution:
Reuse unquote + Windows url2pathname for drive-letter sqlite URL paths inside _parse_db_path (including the four-slash //C:/... shape). Point the CLI sqlite factory at that helper so it cannot drift from SqliteSessionService. Leave relative URIs (sqlite:///test.db) as relative paths so they do not become \test.db. Build the official absolute-URL test with Path.as_posix() so Unix stays ////tmp/... and Windows uses sqlite:///C:/path/to.db.

User impact

Windows users can persist sessions under a drive-letter path, including directories that contain spaces, without getting a differently named database file. The Unix relative and four-slash absolute contracts are unchanged.

Testing Plan

Unit Tests:

• I have added or updated unit tests for my change.
• All focused unit tests pass locally.

pytest tests/unittests/cli/test_service_registry.py::test_create_session_service_sqlite \
  tests/unittests/cli/test_service_registry.py::test_create_session_service_sqlite_ignores_unsupported_kwargs \
  tests/unittests/cli/test_service_registry.py::test_sqlite_session_factory_normalizes_windows_sqlite_uri \
  tests/unittests/cli/test_service_registry.py::test_file_artifact_factory_normalizes_windows_file_uri \
  tests/unittests/sessions/test_session_service.py::test_sqlite_session_service_accepts_sqlite_urls \
  tests/unittests/sessions/test_session_service.py::test_sqlite_session_service_preserves_uri_query_parameters \
  tests/unittests/sessions/test_session_service.py::test_sqlite_session_service_accepts_absolute_sqlite_urls \
  tests/unittests/sessions/test_session_service.py::test_sqlite_session_service_decodes_windows_percent_encoded_path \
  tests/unittests/sessions/test_session_service.py::test_parse_db_path_keeps_relative_sqlite_url_on_windows \
  tests/unittests/sessions/test_session_service.py::test_parse_db_path_windows_drive_and_percent_encoding
10 passed

Manual End-to-End (E2E) Tests:

N/A for this parser fix. The new Windows test creates a real sqlite file at tmp_path / 'adk sessions.db' from sqlite+aiosqlite:///C:/.../adk%20sessions.db and asserts the percent-encoded filename is not created.

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing focused unit tests pass locally with my changes.
• I have manually tested my changes end-to-end (covered by the Windows sqlite file-creation unit test).
• Any dependent changes have been merged and published in downstream modules.

Additional context

file:// artifact URIs already call unquote + url2pathname on Windows. This change brings sqlite session URIs to the same rule. I have signed / will sign the Google CLA as required by CONTRIBUTING.

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