Fix BlocksByRange RPC requests when count is 0

[StefanBratanov]

PR Description

We had an error processing RPC blocks by range request when count is set to 0

Unhandled error while processing request /eth2/beacon_chain/req/beacon_blocks_by_range/2/ssz_snappy","throwable":" java.lang.ArithmeticException: uint64 underflow
 tech.pegasys.teku.infrastructure.unsigned.UInt64.minus(UInt64.java:203)
tech.pegasys.teku.infrastructure.unsigned.UInt64.minus(UInt64.java:157)
tech.pegasys.teku.spec.datastructures.networking.libp2p.rpc.BeaconBlocksByRangeRequestMessage.getMaxSlot(BeaconBlocksByRangeRequestMessage.java:70)

We technically should be able to handle such requests even if they are deemed useless. We have requests limiting so we are not prone to DOS attacks.

Had to also fix BlobSidecarsByRange since maxSlot was not calculated correctly for count == 0

Added tests for both blocks and blob sidecars to ensure they both work.

Did some other small refactors along the way.

Fixed Issue(s)

N/A

Documentation

• I thought about documentation and added the doc-change-required label to this PR if updates are required.

Changelog

• I thought about adding a changelog entry, and added one if I deemed necessary.

[StefanBratanov]

@gfukushima after some discussion with Enrico and Mehdi, we decided to change the logic to be able to handle such requests, just letting you know

[mehdi-aouadi]

LGTM