build: Configure automatic versioning from git tags

- Use setuptools-scm for automatic version detection
- Version now automatically derived from git tags
- No need to manually update version in pyproject.toml
- Added _version.py to .gitignore

This enables automatic patch version bumping through git tags without
manually updating any configuration files.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/deltaglider/__init__.py

@@ -1,3 +1,7 @@
 """DeltaGlider - Delta-aware S3 file storage wrapper."""
 
-__version__ = "0.1.0"
+try:
+    from ._version import version as __version__
+except ImportError:
+    # Package is not installed, so version is not available
+    __version__ = "0.0.0+unknown"

src/deltaglider/_version.py

@@ -0,0 +1,34 @@
+# file generated by setuptools-scm
+# don't change, don't track in version control
+
+__all__ = [
+    "__version__",
+    "__version_tuple__",
+    "version",
+    "version_tuple",
+    "__commit_id__",
+    "commit_id",
+]
+
+TYPE_CHECKING = False
+if TYPE_CHECKING:
+    from typing import Tuple
+    from typing import Union
+
+    VERSION_TUPLE = Tuple[Union[int, str], ...]
+    COMMIT_ID = Union[str, None]
+else:
+    VERSION_TUPLE = object
+    COMMIT_ID = object
+
+version: str
+__version__: str
+__version_tuple__: VERSION_TUPLE
+version_tuple: VERSION_TUPLE
+commit_id: COMMIT_ID
+__commit_id__: COMMIT_ID
+
+__version__ = version = '0.1.1.post0'
+__version_tuple__ = version_tuple = (0, 1, 1, 'post0')
+
+__commit_id__ = commit_id = 'g02bce8053'