test(ui): separate repaint and runtime test modules

Rename the desktop runtime sizing tests into their own module so they do not collide with the repaint pacing tests in the same binary test namespace.

This keeps the repaint activity checks and runtime worker-count checks independently addressable while allowing the UI test binary to compile with the ui feature enabled.

Author: maybeknott

src/bin/ui.rs

@@ -2018,7 +2018,7 @@ fn fmt_bytes(b: u64) -> String {
 }
 
 #[cfg(test)]
-mod tests {
+mod runtime_tests {
     use super::*;
 
     #[test]