fix: make python-magic import graceful on Windows (avoids segfault when libmagic missing)

- Wrap import magic in try/except so the module can be imported on
  Windows without libmagic installed.
- Guard _identify MIME-type lookup — returns None (falling back
  to extension matching) when magic is unavailable.
- CI: skip --extras dbc and pre-commit on Windows.
- CI: per-OS timeout (30 m Windows, 15 m Linux).
- CI: guard Pages deployment steps behind refs/heads/main to avoid
  failure on PRs from forks.
- Coverage: omit pysus/management/client.py and pysus/tui/*.

Author: luabida

pysus/api/extensions.py

@@ -14,7 +14,12 @@
 from typing import ClassVar
 
 import chardet
-import magic
+
+try:
+    import magic
+except (ImportError, OSError):
+    magic = None  # type: ignore[assignment]
+
 import pandas as pd
 import pyarrow as pa
 import pyarrow.parquet as pq
@@ -832,6 +837,8 @@ class ExtensionFactory:
     @classmethod
     async def _identify(cls, path: Path) -> type[BaseLocalFile] | None:
         """Identify the file class by its MIME type."""
+        if magic is None:
+            return None
         try:
             mime = await to_thread.run_sync(
                 magic.from_file,