reverted workers back to 4 in zig perf test

wrk/measure_all.sh

@@ -8,10 +8,10 @@ fi
 
 SUBJECTS="zig-zap go python python-sanic rust-bythebook rust-clean rust-axum csharp cpp-beast"
 
-rm -f wrk/*.perflog
 
 for S in $SUBJECTS; do
     L="$S.perflog"
+    rm -f wrk/$L
     for R in 1 2 3 ; do
         ./wrk/measure.sh $S | tee -a wrk/$L
     done

wrk/zig/main.zig

@@ -19,6 +19,6 @@ pub fn main() !void {
     // start worker threads
     zap.start(.{
         .threads = 4,
-        .workers = 2, // empirical tests: yield best perf on my machine
+        .workers = 4, // empirical tests: yield best perf on my machine
     });
 }