common/test/run-trace: increase iterations for trivial benchmarking.

With an average runtime of 18.7674, this implies 1876ns
per trace, which is far in excess of the 370ns claimed in
doc/developers-guide/tracing-cln-performance.md.

We also add a tag in there, so we measure that!

Results on my laptop:
	real	0m18.524000-19.100000(18.7674+/-0.21)s
	user	0m16.171000-16.833000(16.424+/-0.26)s
	sys	0m2.259000-2.400000(2.337+/-0.059)s

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Author: rustyrussell

common/test/run-trace.c

@@ -13,16 +13,20 @@ int main(int argx, char *argv[])
 	common_setup(argv[0]);
 
 	/* Create a bunch of nested spans to emit. */
-	for(int i=0; i<25000; i++) {
+	for(int i=0; i<2500000; i++) {
 		trace_span_start("a", &a);
+		trace_span_tag(&a, "method", "getrawblockbyheight");
 		trace_span_start("b", &b);
+		trace_span_tag(&b, "method", "getrawblockbyheight");
 
 		trace_span_start("c", &c);
+		trace_span_tag(&c, "method", "getrawblockbyheight");
 		trace_span_end(&c);
 
 		trace_span_end(&b);
 
 		trace_span_start("d", &d);
+		trace_span_tag(&d, "method", "getrawblockbyheight");
 		trace_span_end(&d);
 
 		trace_span_end(&a);