Is your feature request related to a problem? Please describe.

• Current version of SyncPeerPool.Allocate allow allocating a peer for an allocation context, but the same peer can only be allocated once.
• This is slightly inefficient as the during the latency of the request, the peer is not serving the data.

Describe the solution you'd like

• Allow multiple allocation per peer per allocation context. Make the limit configurable, set default to 2.

Describe alternatives you've considered

• Increasing the peer count is inefficient.

Additional context

• base-mainnet struggle to sync due to low number of peer.