fix: __version__ guard catches everything and leaves it unset on failure (#206)

## Summary

`spatialmath/__init__.py`'s `__version__` lookup used a bare `except:
pass`, which has two problems:

- Catches every exception during the `importlib.metadata.version()`
call, not just the "package isn't installed" case
(`PackageNotFoundError`) -- masking anything else that might go wrong
there.
- On failure, `__version__` never gets set at all --
`spatialmath.__version__` raises `AttributeError` rather than giving
something to print, in e.g. a source checkout without an
installed/editable distribution.

Narrowed the `except` to `PackageNotFoundError` and added an explicit
`"unknown"` fallback so the attribute always exists.

## Test plan

- [x] Normal path: `import spatialmath; spatialmath.__version__` still
resolves to the installed version (`1.1.16` locally)
- [x] Failure path: monkeypatched `importlib.metadata.version` to raise
`PackageNotFoundError` and confirmed `__version__` falls back to
`"unknown"` instead of being unset
- [x] New `tests/test_version.py`: asserts it's a non-empty string and
matches `pyproject.toml`'s `version`

Author: petercorke

spatialmath/__init__.py

@@ -51,5 +51,8 @@
     import importlib.metadata
 
     __version__ = importlib.metadata.version("spatialmath-python")
-except:
-    pass
+except importlib.metadata.PackageNotFoundError:
+    # running from a source checkout without an installed/editable
+    # spatialmath-python distribution -- e.g. importing straight from
+    # the repo root
+    __version__ = "unknown"

tests/test_version.py

@@ -0,0 +1,22 @@
+import re
+import unittest
+from pathlib import Path
+
+import spatialmath
+
+
+class TestVersion(unittest.TestCase):
+    def test_version_is_a_non_empty_string(self):
+        self.assertIsInstance(spatialmath.__version__, str)
+        self.assertTrue(spatialmath.__version__)
+
+    def test_version_matches_pyproject(self):
+        pyproject = Path(__file__).parent.parent / "pyproject.toml"
+        match = re.search(r'^version\s*=\s*"([^"]+)"', pyproject.read_text(), re.MULTILINE)
+        self.assertIsNotNone(match, f"couldn't find a version in {pyproject}")
+        self.assertEqual(spatialmath.__version__, match.group(1))
+
+
+# ---------------------------------------------------------------------------------------#
+if __name__ == "__main__":
+    unittest.main()