* chore: cleanup sync serve and reduce log noise
1. Demote a noisy blocksync request error to debug. All this warning
means is that someone is requesting a tipset we don't have.
2. Add a separate warning if we fail to collect a chain. If we have the
tipsets but fail to collect the chain, something is actually wrong.
3. Fix a TODO and return a single CompactedMessages rather than 4
separate values.
* generally reduce the warning to info
It turns out we do fail to gather messages frequently as well, likely
because we have written the tipsets but haven't fetched the messages...
