Add benchmarks

[chrisdickinson]

This adds benchmarks for plugin initialization, writing bytes into a plugin (consume), and reflecting input through a host function back to the host (reflect). The benchmarks run on deno, bun, and node.

I've included a wip! commit (to be removed) that allows the benchmarks to run under Deno 2. However, per #95, Deno 2 lacks any WASI support – it breaks the WASI shim we were using under Deno 1. I'm treating that as a separate issue to be addressed in a subsequent PR.

You should be able to run the benchmarks using just bench (or just bench-node/just bench-bun, just bench-deno)