does not compile with `--target wasm32-unknown-unknown`

``` error[E0308]: mismatched types --> /Users/amitu/.cargo/registry/src/index.crates.io-6f17d22bba15001f/serde_sqlite_jsonb-0.1.0/src/de.rs:103:34 | 103 | usize::from_be_bytes(buf) | -------------------- ^^^ expected an array with a fixed size of 4 elements, found one with 8 elements | | | arguments to this function are incorrect | note: associated function defined here ``` Code is using `usize` in a few places, but since the size of `usize` is not fixed we should convert it to use `u64`/`u32` depending on what is expected based on sqlite jsonb encoding spec.