Implements Spawn in Go and TS

[luiscape]

The Go SDK now supports spawn as follows:

function, err := modal.FunctionLookup(
	context.Background(),
	"libmodal-test-support", "echo_string", modal.LookupOptions{},
)

// Call function using spawn
functionCall, err := function.Spawn(nil, map[string]any{"s": "hello"})

// Get input later
result, err := functionCall.Get(modal.FunctionCallGetOptions{})

// Or cancel Function Call
result, err := functionCall.Cancel(modal.FunctionCallCancelOptions{})

Internally, Remote() is effectively the same as Spawn() + Get().

Equivalent TS implementation:

import { Function_ } from "modal";

const echo = await Function_.lookup("libmodal-test-support", "echo_string");

// Spawn the function with kwargs.
const functionCall = await echo.spawn([], { s: "Hello world!" });
const ret = await functionCall.get();

[ekzhang]

Specific review comments are below, but there are a couple general style changes that I think would make it a better library:

• Follow doc comment conventions: complete sentences, and start with the name of the item being described. https://tip.golang.org/doc/comment
• Fix typos and incomplete comments that trailed off
• Use %w for Go errors instead of %v

These should be pretty quick changes though. After that, happy to collaborate on porting to JS and then we can merge both together.

[luiscape]

@ekzhang thanks for the review. Let me know what you think now.

[ekzhang]

Nice!

[luiscape]

@ekzhang can you take another look? My latest changes implement timeout following our conventions and using the implementation from the Python SDK as reference.