Annotate misc.get_path() while breaking an import cycle.

- `uri` can't be eagerly imported within `misc` without causing a circular import, but is necessary for getting the most currently correct parameter type.

src/rfc3986/misc.py

@@ -18,9 +18,14 @@
 expressions for parsing and validating URIs and their components.
 """
 import re
+import typing as t
 
 from . import abnf_regexp
 
+if t.TYPE_CHECKING:
+    # Break an import loop.
+    from . import uri
+
 # These are enumerated for the named tuple used as a superclass of
 # URIReference
 URI_COMPONENTS = ["scheme", "authority", "path", "query", "fragment"]
@@ -118,7 +123,7 @@
 
 
 # Path merger as defined in http://tools.ietf.org/html/rfc3986#section-5.2.3
-def merge_paths(base_uri, relative_path):
+def merge_paths(base_uri: "uri.URIReference", relative_path: str) -> str:
     """Merge a base URI's path with a relative URI's path."""
     if base_uri.path is None and base_uri.authority is not None:
         return "/" + relative_path