Implement headers fetching via NeoFS BlockFetcher service

[AnnaShaleva]

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

#3515 is missing the ability to fetch block headers from NeoFS.

Describe the solution you'd like

1. Allow to fetch headers. Header size is known (depending on some protocol configuration settings, but in general the size is known at every height). We need to use Blocks objects and use GetRange over every Block object to retrieve header (or just read a fixed-sized slice from Block object stream).
2. Properly add headers to the chain, consider using some buffered queue.
3. Properly integrate headers fetcher with StateSync module.

Describe alternatives you've considered

No alternatives.

[roman-khimov]

Notice that we already have a notion of expectedHeaderSizeWithEmptyWitness, then witness size is just a function of known number of validators.

[AnnaShaleva]

Ref. nspcc-dev/neofs-api#313.