search: Improve performance of zoektIndexedRepos
Created by: efritz
During a hack hour, @keegancsmith and I found that 300ms of global search was being taken by determining which repositories are indexed. This change makes the common case faster and reduces allocations by 98% and wall time by 22% when no branches are specified.
$ benchstat old.txt new.txt
name old time/op new time/op delta
_zoektIndexedRepos-16 151ms ± 5% 118ms ±16% -22.22% (p=0.008 n=5+5)
name old alloc/op new alloc/op delta
_zoektIndexedRepos-16 33.6MB ± 0% 20.8MB ± 0% -38.09% (p=0.008 n=5+5)
name old allocs/op new allocs/op delta
_zoektIndexedRepos-16 407k ± 0% 7k ± 0% -98.37% (p=0.008 n=5+5)