bench: Add --sanity-check flag, use it in make check

The benchmarks are run as part of `make check` for a minimum sanity
check. The actual results are being ignored. So only run them for one
iteration.

This makes the `bench_bitcoin` part take 2m00 instead of 5m20 here.
Which is still too long (imo), but this needs to be solved in the
`WalletLoading*` benchmarks which take that long per iteration.

src/bench/bench.cpp

@@ -57,6 +57,10 @@ void benchmark::BenchRunner::RunAll(const Args& args)
     std::regex reFilter(args.regex_filter);
     std::smatch baseMatch;
 
+    if (args.sanity_check) {
+        std::cout << "Running with --sanity check option, benchmark results will be useless." << std::endl;
+    }
+
     std::vector<ankerl::nanobench::Result> benchmarkResults;
     for (const auto& p : benchmarks()) {
         if (!std::regex_match(p.first, baseMatch, reFilter)) {
@@ -69,6 +73,9 @@ void benchmark::BenchRunner::RunAll(const Args& args)
         }
 
         Bench bench;
+        if (args.sanity_check) {
+            bench.epochs(1).epochIterations(1);
+        }
         bench.name(p.first);
         if (args.min_time > 0ms) {
             // convert to nanos before dividing to reduce rounding errors