Add gearhash package

[coyotte508]

This PR is an experiment to see what a pure-wasm gearhash looks like, using https://www.assemblyscript.org, a language purpose made to generate WASM.

Generating WASM from rust uses a lot of glue, the glue for assembly script seems a lot thinner:

async function instantiate(module, imports = {}) {
  const { exports } = await WebAssembly.instantiate(module, imports);
  return exports;
}
export const {
  memory,
  add,
} = await (async url => instantiate(
  await (async () => {
    const isNodeOrBun = typeof process != "undefined" && process.versions != null && (process.versions.node != null || process.versions.bun != null);
    if (isNodeOrBun) { return globalThis.WebAssembly.compile(await (await import("node:fs/promises")).readFile(url)); }
    else { return await globalThis.WebAssembly.compileStreaming(globalThis.fetch(url)); }
  })(), {
  }
))(new URL("debug.wasm", import.meta.url));

It will also be interesting to compare wasm size between pure wasm & from-rust wasm, as well as provide gearhash to the wider JS/NPM ecosystem.

gearhash is a core component of the xet protocol chunking & hashing and a cool piece of tech!

cc @Wauplin @hanouticelina @assafvayner @rajatarya for viz