Fix deprecated warning in facil.io

[vctrmn]

This PR fixes a compiler warning in the websockets.c file regarding a deprecated non-prototype function declaration. The warning occurs because the new_websocket function is initially declared without a prototype but is later defined with a parameter.

The warning looks like this:

facil.io/lib/facil/http/websockets.c:99:14: warning: a function declaration without a prototype is deprecated in all versions of C and is treated as a zero-parameter prototype in C2x, conflicting with a subsequent definition [-Wdeprecated-non-prototype]
   99 | static ws_s *new_websocket();
      |              ^
facil.io/lib/facil/http/websockets.c:305:14: note: conflicting prototype is here
  305 | static ws_s *new_websocket(intptr_t uuid) {
      |              ^

I encountered this issue while integrating Zap as a zig library in a zig / bazel project (see : https://github.com/vctrmn/zig-text-embeddings-inference)

If you are interested into this topic, I can also upload the BUILD.bazel to showcase how to integrate it.