ensure entrypoint parent folder is in the module search path (#374) (#375)

[This SO answer](https://stackoverflow.com/a/62923810) provides good
detail about the difference between launching a python file (aka `python
app/main.py`) and launching a python module (aka `python -m
widget_store.main`). In particular for this PR, launching a file
automatically adds the file's parent directory to `sys.path` while
launching a module adds the current directory.

`dbos debug` was always ensuring the current directory (represented by
empty string) was in `sys.path`, so it was failing when attempting to
debug a file in a subdirectory. This code fixes that + isolates the
change to `sys.path` to only happen for file launch. Module launch does
not require `sys.path` changes because `dbos debug` is already launching
in the debugger as a module so the current directory will already be on
the path

Co-authored-by: Harry Pierson <[email protected]>

Author: qianl15

dbos/_debug.py

@@ -15,11 +15,11 @@ def __init__(self, module_name: str):
 
 
 def debug_workflow(workflow_id: str, entrypoint: Union[str, PythonModule]) -> None:
-    # include the current directory (represented by empty string) in the search path
-    # if it not already included
-    if "" not in sys.path:
-        sys.path.insert(0, "")
     if isinstance(entrypoint, str):
+        # ensure the entrypoint parent directory is in sys.path
+        parent = str(Path(entrypoint).parent)
+        if parent not in sys.path:
+            sys.path.insert(0, parent)
         runpy.run_path(entrypoint)
     elif isinstance(entrypoint, PythonModule):
         runpy.run_module(entrypoint.module_name)