Optimize allocations in peerFound

[Stebalien]

peerFound is called in response to every single DHT query to update our routing table. However, it allocates quite frequently.

1. We should avoid calling ConvertToStrings every time. Instead, we should cache the string versions of our DHT protocols.
2. We may want an efficient alternative to ps.SupportsProtocols that doesn't allocate.

Together, these account for 22% of allocations (by number, not size) on a bootstrapper.

Besides that, we also do quite a bit of allocation when actually trying to add peers to the routing table (e.g., we get a list of all peers in the bucket to see if we need to kick any out).

[aarshkshah1992]

@Stebalien I'm picking this up. Will get in along with the Routing Table manager refactor.

[Stebalien]

Let's revise that 22% to 66%.

[aarshkshah1992]

Merged in #631.