revert: keep dynamic imports for asgi module to avoid loading for Flask apps

Reverts the direct import of StarletteApplication to keep it as a dynamic
import. This ensures that Flask-only users don't load the asgi module and
its starlette/uvicorn dependencies unnecessarily.

Author: taeold

src/functions_framework/_http/__init__.py

@@ -14,7 +14,6 @@
 
 from flask import Flask
 
-from functions_framework._http.asgi import StarletteApplication
 from functions_framework._http.flask import FlaskApplication
 
 
@@ -36,13 +35,17 @@ def __init__(self, app, debug, **options):
                     self.server_class = FlaskApplication
         else:  # pragma: no cover
             if self.debug:
+                from functions_framework._http.asgi import StarletteApplication
+
                 self.server_class = StarletteApplication
             else:
                 try:
                     from functions_framework._http.gunicorn import UvicornApplication
 
                     self.server_class = UvicornApplication
                 except ImportError as e:
+                    from functions_framework._http.asgi import StarletteApplication
+
                     self.server_class = StarletteApplication
 
     def run(self, host, port):

tests/test_http.py

@@ -154,9 +154,9 @@ def test_httpserver_asgi(monkeypatch, debug, uvicorn_missing, expected):
     }
     options = {"a": pretend.stub(), "b": pretend.stub()}
 
-    import functions_framework._http
+    from functions_framework._http import asgi
 
-    monkeypatch.setattr(functions_framework._http, "StarletteApplication", server_classes["starlette"])
+    monkeypatch.setattr(asgi, "StarletteApplication", server_classes["starlette"])
 
     if uvicorn_missing or platform.system() == "Windows":
         monkeypatch.setitem(sys.modules, "functions_framework._http.gunicorn", None)