Add support for Fastify

[timostamm]

This adds support for the web framework fastify.

With the help of ConnectRouter introduced in #473:

// connect.ts
import { ConnectRouter } from "@bufbuild/connect";

export default function(router: ConnectRouter) {
  // implement rpc Say(SayRequest) returns (SayResponse)
  router.rpc(ElizaService, ElizaService.methods.say, async (req) => ({
    sentence: `you said: ${req.sentence}`,
  }));
}

... plugging services into a fastify server becomes really straight-forward:

// server.ts
import {fastify} from "fastify";
+ import routes from "connect.js";
+ import { fastifyConnectPlugin } from "@bufbuild/connect-fastify";

const server = fastify({
  http2: true,
});

+ await server.register(fastifyConnectPlugin, { 
+  routes 
+ });

await server.listen();

With this, we are also changing the approach taken for @bufbuild/connect-node, and provide a single adapter function for vanilla Node.js servers, that also makes use of ConnectRouter, similar to the example for fastify above:

// server.ts
import * as http2 from "http2";
+ import routes from "connect.js";
+ import { connectNodeAdapter } from "@bufbuild/connect-node";

http2.createServer(
+ connectNodeAdapter({ routes }) // responds with 404 for other requests
).listen(8080);

Other changes:

• updates all package-level READMEs
• deprecated all re-exports from @bufbuild/connect(-core) - we ask you kindly to simply change the import to @bufbuild/connect
• updates connect-node-test to run all tests against a fastify h2c server in addition
• updates the example to use a vanilla http2 server instead of express for better interop with gRPC clients - we may want to spice this example up in the future