Add wasm64 builds to CI and publish

[texodus]

This PR enabled a parallel Memory64 build of @perspective-dev/server, which allows allocating more than 4gb in Perspective wasm.

init_server accepts both binaries at once — register each as a thunk and only the selected binary is ever downloaded. The wasm64 binary is used whenever the browser supports Memory64; registering only the wasm32 binary (as above) opts out.

perspective.init_server({
    wasm32: () => fetch(SERVER_WASM),
    wasm64: () => fetch(SERVER_WASM64),
});