get next collation to fetch

### Description

Using the claim queue state this method should retrieve the next collation to issue a request for

### Links

https://github.com/paritytech/polkadot-sdk/blob/c679ed79a1de575d4c3d5b8878b3e401b024f2f2/polkadot/node/network/collator-protocol/src/validator_side/mod.rs#L2179

Start with the referenced validator_side/mod.rs entry point at line 2179 and inspect how the claim queue state is used to select the next collation. Trace the corresponding Gossamer method and determine how it should retrieve the next collation for a request; done means the method follows the claim queue state and returns the expected next collation.

Written by the indexing model from the issue text.