# Description

Follow-up to https://github.com/paritytech/polkadot-sdk/pull/5469 and
mostly covering https://github.com/paritytech/polkadot-sdk/issues/5333.

The primary change here is that syncing strategy is no longer created
inside of syncing engine, instead syncing strategy is an argument of
syncing engine, more specifically it is an argument to `build_network`
that most downstream users will use. This also extracts addition of
request-response protocols outside of network construction, making sure
they are physically not present when they don't need to be (imagine
syncing strategy that uses none of Substrate's protocols in its
implementation for example).

This technically allows to completely replace syncing strategy with
whatever strategy chain might need.

There will be at least one follow-up PR that will simplify
`SyncingStrategy` trait and other public interfaces to remove mentions
of block/state/warp sync requests, replacing them with generic APIs,
such that strategies where warp sync is not applicable don't have to
provide dummy method implementations, etc.

## Integration

Downstream projects will have to write a bit of boilerplate calling
`build_polkadot_syncing_strategy` function to create previously default
syncing strategy.

## Review Notes

Please review PR through individual commits rather than the final diff,
it will be easier that way. The changes are mostly just moving code
around one step at a time.

# Checklist

* [x] My PR includes a detailed description as outlined in the
"Description" and its two subsections above.
* [x] My PR follows the [labeling requirements](

https://github.com/paritytech/polkadot-sdk/blob/master/docs/contributor/CONTRIBUTING.md#Process
) of this project (at minimum one label for `T` required)
* External contributors: ask maintainers to put the right label on your
PR.
* [x] I have made corresponding changes to the documentation (if
applicable)