Add sync and workerd entrypoints for Cloudflare runtimes

[calclavia]

Summary

Cloudflare Workers and other workerd-style runtimes import .wasm assets as precompiled WebAssembly.Module objects, while this package currently only publishes the wasm-pack --target bundler entrypoint. That forces downstream consumers to patch the generated loader or maintain wrapper packages just to instantiate biscuit-wasm in Cloudflare-style runtimes.

This PR upstreams that runtime support without changing the existing bundler path.

• add a new @biscuit-auth/biscuit-wasm/sync entrypoint with initSync(...) for runtimes that can provide a precompiled WebAssembly.Module or raw wasm bytes
• add a workerd export condition plus an explicit @biscuit-auth/biscuit-wasm/workerd subpath that initializes from biscuit_bg.wasm automatically
• generate the manual-init runtime files during prepare-package, discovering snippet import paths from the built package instead of hardcoding wasm-bindgen hash directories in source
• expose ./module/biscuit_bg.js and ./module/biscuit_bg.wasm subpaths for custom loaders, and document the new runtime options in the README
• add a JS regression test that exercises the new sync entry against a precompiled WebAssembly.Module

Test plan

• npm run check-format
• cargo fmt --check
• cargo clippy -- -D warnings
• npm run prepare-package
• cd js-tests && npm install && npm test
• cd examples/node && npm install && npm start