Fix class names not being null-terminated

[Arshia001]

The call to JS_InitClass was using Self::NAME.as_ptr() which is a rust string and is not properly null-terminated, resulting in class names overflowing into neighboring data resulting in names such as:

String("AbortSignalUninitialised ClassExpected Headersa Display implementation returned an error unexpectedly/rustc/5680fa18feaa87f3ff04063800aec256c3d4b4be/library/alloc/src/string.rs/Users/arshia/.cargo/registry/src/index.crates.io-6f17d22bba15001f/http-0.2.9/src/extensions.rs/Users/arshia/.cargo/registry/src/index.crates.io-6f17d22bba15001f/http-0.2.9/src/request.rswant called after cancel/Users/arshia/.cargo/registry/src/index.crates.io-6f17d22bba15001f/want-0.3.1/src/lib.rs/rustc/5680fa18feaa87f3ff04063800aec256c3d4b4be/library/alloc/src/slice.rs/Users/arshia/.cargo/registry/src/index.crates.io-6f17d22bba15001f/bytes-1.5.0/src/buf/buf_impl.rs/Users/arshia/.cargo/git/checkouts/hyper-c8030e08a3cfc43d/1e517b1/src/proto/h1/role.rssetting h1 header read timeout timerresetting h1 header read timeout timer/Users/arshia/.cargo/git/checkouts/tokio-2eb71367495b4da5/2be2588/tokio/src/net/tcp/socket.rs")

This PR uses a CString to fix the issue.