Tighten up typing on resolve_path

Hard to be non-concrete types with the approach we are using here

Author: ndevenish

src/dxtbx/serialize/filename.py

@@ -2,19 +2,15 @@
 
 import glob
 import os
-from typing import AnyStr, TypeVar, overload
+from pathlib import Path
+from typing import TypeVar
 
 from dxtbx.sequence_filenames import template_string_to_glob_expr
 
-T = TypeVar("T", AnyStr, os.PathLike)
+T = TypeVar("T", str, Path)
 
 
-@overload
-def resolve_path(path: T, directory: AnyStr | os.PathLike | None) -> T:
-    pass
-
-
-def resolve_path(path: T, directory: AnyStr | os.PathLike | None = None) -> T:
+def resolve_path(path: T, directory: str | os.PathLike | None = None) -> T:
     """Resolve a file path.
 
     First expand any environment and user variables. Then create the absolute
@@ -25,17 +21,16 @@ def resolve_path(path: T, directory: AnyStr | os.PathLike | None = None) -> T:
       links
 
     Returns:
-        str: The absolute path to the file to read, if accessible, otherwise
-            return the original path..
+        The absolute path to the file to read, if accessible, otherwise
+        return the original path.
     """
 
     assert path, "Believe this is overly defensive, check if we ever rely on"
     if not path:
-        return ""
-    path = str(path)
-    trial_path = os.path.expanduser(os.path.expandvars(path))
+        return path
+    trial_path = os.path.expanduser(os.path.expandvars(str(path)))
     if directory and not os.path.isabs(trial_path):
-        trial_path = os.path.join(str(directory), trial_path)
+        trial_path = os.path.join(os.fspath(directory), trial_path)
     trial_path = os.path.abspath(trial_path)
     if glob.glob(template_string_to_glob_expr(trial_path)):
         return type(path)(trial_path)