[Optimize] Add guards for processing unconfirmed solutions

[raychu86]

Motivation

This PR adds a few changes to improve syncing and reduce network spam:

1. Clients perform solution verification in POST /broadcast/solution prior to solution propagation.
   • This reduces the propagation of invalid solutions on the network.
2. Nodes do not process incoming unconfirmed solutions if they are syncing.
   • This reduces the resource load of nodes and lets them focus on syncing.
3. Nodes do not process incoming unconfirmed transactions if they are syncing
   • This reduces the resource load of nodes and lets them focus on syncing.

[iamalwaysuncomfortable]

The following measures are being done to test this

• [x] Run a 30 client, 10 validator devnet with a high load of solution spam
• [ ] Analyze the results

The devnet run has completed, and analysis of it is forthcoming.