Report tip status in BlockInfo

[SupernaviX]

Description

Add a tip_slot field to BlockInfo, indicating which slot "the tip" is currently at. This field is None by default and while e.g. syncing from mithril, but we populate it while transmitting blocks from the ChainSync mini-protocol. This field currently refers to the tip of the chain of whichever peer we've decided to follow.

Also adds a test for a regression from an older implementation of PeerNetworkInterface.

Related Issue(s)

Completes #422

How was this tested?

I synced the node with preview after booting from a mithril snapshot, confirming that

• it did not report a tip while restoring from the snapshot
• it reported a tip in the future while catching up
• it reported a tip in the present (or past) once caught up

Checklist

• My code builds and passes local tests
• I added/updated tests for my changes, where applicable
• I updated documentation (if applicable)
• CI is green for this PR

Impact / Side effects

An extra optional u64 in BlockInfo which gets passed everywhere

Reviewer notes / Areas to focus

The only non-mechanical changes are updates to BlockInfo and PeerNetworkInterface

[whankinsiv]

Looks good!