Collator protocol validator side refactoring ideas

[tdimitrov]

For further refactoring:

• [ ] Let's avoid querying the per_relay_parent map again and again if we can pass it as a param to the function. it saves us some superfluous error handling that is already handled a level above. _Originally posted by @alindima in https://github.com/paritytech/polkadot-sdk/pull/4880#discussion_r1860666690_
• [ ] In Collations fetching_from really should be a part of the CollationStatus::Fetching() status variant Originally posted by @alindima in https://github.com/paritytech/polkadot-sdk/pull/4880/files#r1860614933
• [ ] Avoid calculating claim queue state each time it is needed (unfulfilled_claim_queue_entries and the code in ensure_seconding_limit_is_respected). Instead keep ClaimQueueState for all paths in State, keep them up to date by marking seconded and pending canddiates accordingly, and have it ready for use when needed. - https://github.com/paritytech/polkadot-sdk/pull/4880/files#r1861728429 and https://github.com/paritytech/polkadot-sdk/pull/4880/files#r1861727967

[alindima]

Generally it would also help if the code were less procedural and better structured in objects with methods