Refactor pyexec (#1318)

This is some refactoring I did on the way towards resolving pyscript#1313.
I added a new _run_pyscript Python function which executes the code
inside a context manager that sets the display target. We can then
return a JS object wrapper directly from Python.

I moved the "installation" of the pyscript module to loadInterpreter,
and pyimport pyscript_py there and give it a type. This avoids a bunch
of creating and deleting of proxies for pyscript_py and allows us to
give it a type once and for all.

I also did some minor logic cleanup in a few places.

pyscriptjs/environment.yml

@@ -3,7 +3,7 @@ channels:
     - conda-forge
     - microsoft
 dependencies:
-    - python=3.9
+    - python=3.11
     - pip
     - pytest=7
     - nodejs=16
@@ -18,3 +18,7 @@ dependencies:
           - playwright
           - pytest-playwright
           - pytest-xdist
+          # We need Pyodide and micropip so we can import them in our Python
+          # unit tests
+          - pyodide_py==0.22
+          - micropip==0.2.2