fix(ws): fix zlib version mismatch on Windows (segfault) (#25538)

## Summary

Fixes #24593 - WebSocket segfault on Windows when publishing large
messages with `perMessageDeflate: true`.
Also fixes #21028 (duplicate issue).
Also closes #25457 (alternative PR).

**Root cause:** 

On Windows, the C++ code was compiled against system zlib headers
(1.3.1) but linked against Bun's vendored Cloudflare zlib (1.2.8).

This version mismatch caused `deflateInit2()` to return
`Z_VERSION_ERROR` (-6), leaving the deflate stream in an invalid state.
All subsequent `deflate()` calls returned `Z_STREAM_ERROR` (-2),
producing zero output, which then caused an integer underflow when
subtracting the 4-byte trailer → segfault in memcpy.

**Fix:** 

Add `${VENDOR_PATH}/zlib` to the C++ include paths in
`cmake/targets/BuildBun.cmake`. This ensures the vendored zlib headers
are found before system headers, maintaining header/library version
consistency.

This is a simpler alternative to #25457 which worked around the issue by
using libdeflate exclusively.

## Test plan

- [x] Added regression test `test/regression/issue/24593.test.ts` with 4
test cases:
  - Large ~109KB JSON message publish (core reproduction)
  - Multiple rapid publishes (buffer corruption)
  - Broadcast to multiple subscribers
  - Messages at CORK_BUFFER_SIZE boundary (16KB)
- [x] Tests pass on Windows (was crashing before fix)
- [x] Tests pass on macOS

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

cmake/targets/BuildBun.cmake

@@ -872,6 +872,7 @@ target_include_directories(${bun} PRIVATE
   ${CODEGEN_PATH}
   ${VENDOR_PATH}
   ${VENDOR_PATH}/picohttpparser
+  ${VENDOR_PATH}/zlib
   ${NODEJS_HEADERS_PATH}/include
   ${NODEJS_HEADERS_PATH}/include/node
 )