When searching the caches don't copy the ids, instead inline the loop.
```
Benchmark_bucketMetacache_findCache-32 19200 63490 ns/op 8303 B/op 5 allocs/op
Benchmark_bucketMetacache_findCache-32 20338 58609 ns/op 111 B/op 4 allocs/op
```
Add a reasonable, but still the simplistic benchmark.
Bonus - make nicer zero alloc logging
Klaus Post