Add benchmark and optimize performance of common functions

[dmcgowan]

Currently we use URI() for comparison checks which causes unnecessary allocations. Directly comparing the values or pointers greatly improves performance.

Another additional speedup is achieved by doing the disabled set check after the other checks, which are faster and often false when scanning over the whole registry.

Locally, I see a 20x speed improvement on graph and 40x on uniqueness check and allocations drop to zero or near zero. Its harder to measure due to init across 50+ plugins in containerd, but with this change I see a 25% speedup in containerd startup on the same machine (20ms to 15ms avg)

benchmark              old ns/op     new ns/op     delta
BenchmarkGraph-14      645422        28617         -95.57%
BenchmarkUnique-14     895           23.8          -97.34%

benchmark              old allocs     new allocs     delta
BenchmarkGraph-14      15020          8              -99.95%
BenchmarkUnique-14     14             0              -100.00%

benchmark              old bytes     new bytes     delta
BenchmarkGraph-14      725768        5192          -99.28%
BenchmarkUnique-14     672           0             -100.00%