fix(tests): move lib tests into adk/, fix dev install via pkgutil.extend_path

Follows up the slim/heavy split with the test relocations + dev-install
plumbing that should have been part of the original commit:

- Move tests/lib/* and tests at tests/ root that exercise lib code
  (test_function_tool.py, test_model_utils.py, test_header_forwarding.py)
  into adk/tests/. Tests now live with the code they test. The Path-based
  source references in test_claude_agents_*.py (`_SRC = parents[2] / "src"`)
  resolve correctly to adk/src/ via the new location.

- Fix test_function_tool.py's broken `src.agentex.lib.*` import — switch
  to the installed-package path `agentex.lib.*` so it works against the
  editable install.

- Add `from pkgutil import extend_path; __path__ = extend_path(...)` to
  src/agentex/__init__.py. This is the load-bearing fix for dev workflow:
  without it, two editable installs (slim at root, heavy at adk/) each
  contributing files to `agentex/` get only the first source dir in
  `agentex.__path__`, so `import agentex.lib.*` fails. With it, Python
  discovers both source trees and the namespace merges. Wheel installs
  (production) already worked because both wheels' files land in the same
  site-packages/agentex/ directory.

- scripts/bootstrap: after `rye sync`, also `pip install -e ./adk` so
  agentex-sdk's deps land in the dev venv. agentex-sdk-client is already
  installed via the root sync, so adk's dep on it resolves to the local
  editable install (no PyPI lookup needed).

- pyproject.toml [tool.pytest.ini_options].testpaths includes "adk/tests".
- pyproject.toml [tool.ruff.lint.per-file-ignores] extends test-friendly
  ignores to adk/tests/.
- Drop the rye workspace config — pkgutil.extend_path + explicit pip
  install -e ./adk in bootstrap gives the same dev experience without
  rye-workspace-version-mismatch quirks.
- .github/workflows/ci.yml: lint + test jobs call ./scripts/bootstrap
  instead of `rye sync` directly; build job builds both packages.

Self-review took: I shipped the file move without running the test suite
locally — that's why CI broke on PR #370. Mea culpa. The functional design
is correct; the rollout was sloppy. Verified locally:
- `ruff check .` → All checks passed
- `pytest --collect-only adk/tests/` → 100+ tests collect cleanly
- `pytest adk/tests/test_function_tool.py` → 10 passed
- Dev install (`pip install -e .` + `pip install -e ./adk`):
  `from agentex import Agentex` and `from agentex.lib.* import …` both work

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: max-parke-scale

.github/workflows/ci.yml

@@ -32,7 +32,7 @@ jobs:
           RYE_INSTALL_OPTION: '--yes'
 
       - name: Install dependencies
-        run: rye sync --all-features
+        run: ./scripts/bootstrap
 
       - name: Run lints
         run: ./scripts/lint
@@ -57,11 +57,14 @@ jobs:
           RYE_INSTALL_OPTION: '--yes'
 
       - name: Install dependencies
-        run: rye sync --all-features
+        run: ./scripts/bootstrap
 
-      - name: Run build
+      - name: Run build (slim agentex-sdk-client)
         run: rye build
 
+      - name: Run build (ADK overlay agentex-sdk)
+        run: (cd adk && rye build)
+
       - name: Get GitHub OIDC Token
         if: |-
           github.repository == 'stainless-sdks/agentex-sdk-python' &&