Implements JS Blob API in Python SDK

[dom96]

The big change here is the addition of the Blob API. But there are also some other improvements/fixes:

• Each class instance now exposes a js_object property which returns its underlying JS object.
• The FormData API is now compatible with the multidict package's API
• The FormData API can now accept Blobs and returns the Python Blobs too

Test Plan

$ bazel run @workerd//src/workerd/server/tests/python:sdk/sdk

[hoodmane]

Do you still think we should do this? I thought the duplicate values are combined with a comma. How does http.client.HTTPMessage handle values with a comma in them?

[dom96]

It's not super important, but it would be nice. Splitting values by comma is pretty bleh as far as API design.

But I guess on the other hand that is what JS' Headers expects so maybe it's fine.

[hoodmane]

Seems like it might be better to be explicit here:

Suggested change

	**options: Unpack[BlobKwargs],
	):
	if "content_type" in options:
	options["type"] = options["content_type"]
	if "endings" in options:
	options["endings"] = str(options["endings"])
	content_type: str | None = None,
	endings: BlobEnding | str | None = None
	):
	if endings:
	endings = str(endings)

and then:

    js.Blob.new(args, type=content_type, endings=endings)

Also, I am pretty sure that you don't need to_js for args.

[dom96]

Also, I am pretty sure that you don't need to_js for args.

You do, I get this otherwise: pyodide.ffi.JsException: TypeError: Failed to construct 'Blob': constructor parameter 1 is not of type 'Array'.

[hoodmane]

That's unfortunate. There's been discussion before whether we should make Array.isArray() return true on a Python list. Not sure whether it would fix this error message. I also don't remember why I didn't do it -- it's possible I just never got to it, or that there was some problem it caused.

[hoodmane]

Looking pretty good now, thanks @dom96. I have one last remark.