Move pyodide to a web worker (#1333)

This PR adds support for optionally running pyodide in a web worker:

- add a new option config.execution_thread, which can be `main` or `worker`. The default is `main`

- improve the test machinery so that we run all tests twice, once for `main` and once for `worker`

- add a new esbuild target which builds the code for the worker

The support for workers is not complete and many features are still missing: there are 71 tests which are marked as `@skip_worker`, but we can fix them in subsequent PRs.

The vast majority of tests fail because js.document is unavailable: for it to run transparently, we need the "auto-syncify" feature of synclink.


Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com>
Co-authored-by: Madhur Tandon <20173739+madhur-tandon@users.noreply.github.com>

pyscriptjs/src/remote_interpreter.ts

@@ -105,7 +105,6 @@ export class RemoteInterpreter extends Object {
         this.interface = Synclink.proxy(
             await loadPyodide({
                 stdout: (msg: string) => {
-                    // TODO: add syncify when moved to worker
                     stdio.stdout_writeline(msg).syncify();
                 },
                 stderr: (msg: string) => {
@@ -114,6 +113,8 @@ export class RemoteInterpreter extends Object {
                 fullStdLib: false,
             }),
         );
+        this.interface.registerComlink(Synclink);
+        // eslint-disable-next-line @typescript-eslint/no-unsafe-assignment
         this.FS = this.interface.FS;
         // eslint-disable-next-line @typescript-eslint/no-unsafe-member-access
         this.PATH = (this.interface as any)._module.PATH;