Improve handling of the %run magic for local runs (#1612)

## Changes
- Strip quotes around filenames
- Use raw strings for the project root and filename (avoid unicode
issues for paths with `\u` sequences - e.g. `\User\***` on Windows)



Fixes #1611

## Tests

Existing integ tests

Author: ilia-db

packages/databricks-vscode/resources/python/00-databricks-init.py

@@ -316,15 +316,16 @@ def handle(lines: List[str]):
                 if len(rest) == 0:
                     return lines
 
-                filename = rest[0]
+                # Strip whitespace or possible quotes around the filename
+                filename = rest[0].strip('\'" ')
 
                 for suffix in ["", ".py", ".ipynb", ".ipy"]:
                     if os.path.exists(os.path.join(os.getcwd(), filename + suffix)):
                         filename = filename + suffix
                         break
 
                 return [
-                    f"with databricks_notebook_exec_env('{cfg.project_root}', '{filename}') as file:\n",
+                    f"with databricks_notebook_exec_env(r'{cfg.project_root}', r'{filename}') as file:\n",
                     "\t%run -i {file} " + lines[0].partition('%run')[2].partition(filename)[2] + "\n"
                 ]