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/tests/integration/test_async.py

@@ -1,4 +1,4 @@
-from .support import PyScriptTest
+from .support import PyScriptTest, skip_worker
 
 
 class TestAsync(PyScriptTest):
@@ -87,6 +87,7 @@ class TestAsync(PyScriptTest):
             "b func done",
         ]
 
+    @skip_worker("FIXME: display()")
     def test_multiple_async_multiple_display_targeted(self):
         self.pyscript_run(
             """
@@ -119,6 +120,7 @@ class TestAsync(PyScriptTest):
         inner_text = self.page.inner_text("html")
         assert "A0\nA1\nB0\nB1" in inner_text
 
+    @skip_worker("FIXME: display()")
     def test_async_display_untargeted(self):
         self.pyscript_run(
             """