feat: support custom Tokio worker thread names

  Auto-discover worker threads when the default tokio-runtime-w prefix
  finds nothing by scanning /proc for the largest thread group matching
  {name}-{N} patterns. Add --workers flag as explicit override. On
  failure, log all thread names with a suggested prefix.

  Add THREAD_NAME env var to demo-server for testing custom names.

Author: cong-or

hud/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "hud"
-version = "0.4.4"
+version = "0.4.5"
 edition = "2021"
 license = "MIT"