PollWS is deprecated in favor of PollNet (https://github.com/probable-basilisk/pollnet), which provides better functionality (in particular: secure websockets, a websocket server, and an HTTP server) with a mostly similar API.
Single DLL, C api, polling-based websocket client. Basically a wrapper to the "ws" Rust library.
This is probably the worst piece of Rust code ever written.
Assuming you're on a 64 bit machine, building for 64 bit:
cargo build --release
However to use this from a 32 bit Windows binary (e.g., Noita), you'll need to build for 32 bit:
rustup target add i686-pc-windows-msvc
cargo build --target=i686-pc-windows-msvc --release
The resulting .dll will end up in target/i686-pc-windows-msvc/release/pollws.dll.