Support size-delimited messages

[timostamm]

This implements support for size-delimited messages described in protocolbuffers/protobuf#10229

A size-delimited message is a varint size in bytes, followed by exactly that many bytes of a message serialized with the binary format. This implementation is compatible with the counterparts in C++, Java, Go, and others.

You create such a message with protoDelimited.enc:

import { protoDelimited } from "@bufbuild/protobuf";

const bytes = protoDelimited.enc(new User({ firstName: "John" }));
const user = protoDelimited.dec(User, bytes);

With protoDelimited.decStream, you can parse messages from a stream. The method expects an AsyncIterable<Uint8Array> as a stream input, so it works with Node.js streams out of the box, and can be easily adapted to other stream APIs:

import { protoDelimited } from "@bufbuild/protobuf";
import { createReadStream, createWriteStream } from "fs";
import { tmpdir } from "os";
import { join } from "path";

// Let's write a couple of messages to a file
const ws = createWriteStream("protoDelimited.bin", {encoding: "binary"});
ws.write(protoDelimited.enc(new User({ firstName: "John" })));
ws.write(protoDelimited.enc(new User({ firstName: "Max" })));
ws.write(protoDelimited.enc(new User({ firstName: "Max" })));
ws.end();
ws.close();

// Now we can parse them from the stream
const readStream = createReadStream("protoDelimited.bin");
for await (const user of protoDelimited.decStream(User, readStream)) {
  console.log(user);
}

[akshayjshah]

I'm almost completely unable to parse the actual code, but the unit tests look nice! As long as we're following the proposal in the discussion you linked, this lgtm. (I assume that short names like enc and dec match the rest of the code.)

[timostamm]

Have added the decStream method to the object after running some tests. This PR also adds documentation now.