fix: sync _version.py to 0.15.4, and guard the pair (#39)

`#38` bumped `pyproject.toml` to 0.15.4 but left `src/sonilo/_version.py` on
0.15.3. `__version__` ships as the `x-sonilo-client-version` header, so a 0.15.4
release would have had every client on it identify itself as 0.15.3.

Nothing caught it: the existing version tests compare the header to
`__version__`, which stays self-consistent however stale it is, and no test
compared either to pyproject. The release commits have always bumped both by
hand (a41a37c, 2c78bd8), which works right up until someone bumps only one.

Adds the missing comparison so the next one-sided bump fails in CI instead of
on PyPI. sonilo-cli is unaffected — its own version and its
`sonilo>=0.15.0,<0.16` pin both still hold.


Claude-Session: https://claude.ai/code/session_01SFP9xPKwk2S1Qjmk5krx6h

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: spencer-zqian

src/sonilo/_version.py

@@ -1 +1 @@
-__version__ = "0.15.3"
+__version__ = "0.15.4"

tests/test_client_identity.py

@@ -80,3 +80,25 @@ async def test_async_defaults_to_sdk_python():
     headers = route.calls.last.request.headers
     assert headers["x-sonilo-client"] == "sdk-python"
     assert headers["x-sonilo-client-version"] == __version__
+
+
+def test_version_module_matches_pyproject():
+    """`__version__` ships as the x-sonilo-client-version header, so a release
+    whose _version.py lagged pyproject.toml would have every client on that
+    version identify itself as the previous one.
+
+    Nothing caught that before: the other version tests compare the header to
+    `__version__`, which stays self-consistent however stale it is. 0.15.4 went
+    out with _version.py still on 0.15.3 for exactly that reason."""
+    import re
+    from pathlib import Path
+
+    from sonilo._version import __version__
+
+    # Read the line, not tomllib: this package supports 3.9 and tomllib is
+    # 3.11+, so parsing properly would make the guard skip on exactly the
+    # oldest interpreter CI runs.
+    pyproject = Path(__file__).resolve().parent.parent / "pyproject.toml"
+    text = pyproject.read_text(encoding="utf-8")
+    declared = re.search(r'(?m)^version = "([^"]+)"', text).group(1)
+    assert __version__ == declared