fix: --target wasm32-unknown-unknown for loro crate (getrandom dep)

[synoet]

Running

cd crates/loro && cargo build --target wasm32-unknown-unknown

Gives the following:

error: the wasm*-unknown-unknown targets are not supported by default, you may need to enable the "js" feature. For more information see: https://docs.rs/getrandom/#webassembly-support
   --> /Users/synoet/.cargo/registry/src/index.crates.io-6f17d22bba15001f/getrandom-0.2.15/src/lib.rs:342:9
    |
342 | /         compile_error!("the wasm*-unknown-unknown targets are not supported by \
343 | |                         default, you may need to enable the \"js\" feature. \
344 | |                         For more information see: \
345 | |                         https://docs.rs/getrandom/#webassembly-support");
    | |________________________________________________________________________^

error[E0433]: failed to resolve: use of undeclared crate or module `imp`
   --> /Users/synoet/.cargo/registry/src/index.crates.io-6f17d22bba15001f/getrandom-0.2.15/src/lib.rs:398:9
    |
398 |         imp::getrandom_inner(dest)?;
    |         ^^^ use of undeclared crate or module `imp`

Conditionally enabling the js feature for getrandom in loro-internal when target architecture is wasm-32 fixes the issue.

Allows using the loro crate in projects that compile to wasm32-unknown-unknown like cloudflare's worker-rs, which was the use case where I ran into this issue at first.

[zxch3n]

Thanks!