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/src/interpreter_client.ts

@@ -45,13 +45,23 @@ export class InterpreterClient extends Object {
     }
 
     /**
-     * delegates the code to be run to the underlying interface of
-     * the remote interpreter.
-     * Python exceptions are turned into JS exceptions.
-     * */
+     * Run user Python code. See also the _run_pyscript docstring.
+     *
+     * The result is wrapped in an object to avoid accidentally awaiting a
+     * Python Task or Future returned as the result of the computation.
+     *
+     * @param code the code to run
+     * @param id The id for the default display target (or undefined if no
+     * default display target).
+     * @returns Either:
+     * 1. An Object of the form {result: the_result} if the result is
+     *    serializable (or transferable), or
+     * 2. a Synclink Proxy wrapping an object of this if the result is not
+     *    serializable.
+     */
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
-    async run(code: string): Promise<{ result: any }> {
-        return await this._remote.run(code);
+    async run(code: string, id?: string): Promise<{ result: any }> {
+        return this._remote.pyscript_py._run_pyscript(code, id);
     }
 
     /**