fix bindings/wasm wal file creation by implementing generate_random_number

[OwenDelahoy]

In binding/wasm generate_random_number's implementation depends on an external function Math_random which does not exist

A related error can be observed when viewing limbo-opfs-test.html without an existing database. (Note: it will execute successfully if the wal file already exists, so you may wish view the html in a private/incognito session to ensure an existing file from a previous run is not used)

This error occurs upon wal file creation as it uses generate_random_number for salt_1 and slat_2 in the header
https://github.com/tursodatabase/limbo/blob/main/core/storage/wal.rs#L764-L773)

This PR uses the same implementation as other platforms

core/io/unix.rs
https://github.com/tursodatabase/limbo/blob/main/core/io/unix.rs#L259-L263

core/io/windows.rs
https://github.com/tursodatabase/limbo/blob/main/core/io/windows.rs#L40-L44

The library getrandom supports wasm and uses Crypto.getRandomValues for the implementation in wasm.