Extract warp sync strategy from ChainSync (#2467)

Extract `WarpSync` (and `StateSync` as part of warp sync) from
`ChainSync` as independent syncing strategy called by `SyncingEngine`.
Introduce `SyncingStrategy` enum as a proxy between `SyncingEngine` and
specific syncing strategies.

## Limitations
Gap sync is kept in `ChainSync` for now because it shares the same set
of peers as block syncing implementation in `ChainSync`. Extraction of a
common context responsible for peer management in syncing strategies
able to run in parallel is planned for a follow-up PR.

## Further improvements
A possibility of conversion of `SyncingStartegy` into a trait should be
evaluated. The main stopper for this is that different strategies need
to communicate different actions to `SyncingEngine` and respond to
different events / provide different APIs (e.g., requesting
justifications is only possible via `ChainSync` and not through
`WarpSync`; `SendWarpProofRequest` action is only relevant to
`WarpSync`, etc.)

---------

Co-authored-by: Aaro Altonen <48052676+altonen@users.noreply.github.com>

substrate/zombienet/0003-block-building-warp-sync/test-block-building-warp-sync.zndsl

@@ -27,6 +27,8 @@ dave: reports block height is at least {{DB_BLOCK_HEIGHT}} within 60 seconds
 dave: reports block height is greater than {{DB_BLOCK_HEIGHT}} within 60 seconds
 
 dave: log line matches "Warp sync is complete" within 60 seconds
+# State sync is logically part of warp sync
+dave: log line matches "State sync is complete" within 60 seconds
 dave: log line matches "Block history download is complete" within 10 seconds
 
 dave: reports substrate_beefy_best_block is at least {{DB_BLOCK_HEIGHT}} within 180 seconds