libsql will not build on windows

[gregtbrown]

the code at: https://github.com/tursodatabase/libsql/blob/main/libsql-ffi/build.rs#L42

should be (based on the build platform) something like:

 Command::new("xcopy")
     .arg("/S")
     .arg(format!("{dir}\\{bindgen_rs_path}"))
     .arg(&out_path)
     .output()
     .unwrap();

I hacked this into the files installed by cargo add libsql and it allowed it to build and run successfully.