fix: claimed in staking payout endpoint

[Imod7]

Description

New PR that is replacing the following quite old & outdated PRs :

• fix: added staking.claimed() in replacement of staking.ledger().legacyClaimedRewards #1436
• fix: staking payouts claimed with new logic & statuses #1457

All changes in the current PR should be aligned with the changes merged & final logic implemented in the #1445 PR of the staking-info endpoint. In the 1445 PR, two very useful guides were added to explain the finalized logic for the field claimed:

1. the hackMD: "Staking PR - claimed field - Guide".
2. the README: "STAKING_IMPLEMENTATION_DETAILS.md".

which can be helpful here too.

Changes

• Renamed fetchCommissionAndLedger to fetchCommissionLedgerAndClaimed because it now also returns claimedRewards.
• The logic for claimedRewards is based on this PR for the staking-info endpoint.
• The claimed field returned from staking-payouts is no longer a boolean value; It now has different statuses.
• A status called undefined was added which means that with the current information, we cannot determine if the rewards of the era were claimed, unclaimed or partially claimed.
  • an example is the case when the only available info is lastReward and it is null, then claimed is set to undefined
• With the old code, if none of the checks/properties/calls could define the claimedfield, we would continue/skip that era and do not return any info about that era. Now we don't, we just set the claimed field as undefined.
• Some of the logic was moved from function deriveEraPayouts to fetchCommissionAndLedger.
• The case era < 518 && chain is Kusama is still working as expected. The era in this case is "automatically" considered as claimed.

Testing

• Tested cases claimed and unclaimed
• Tested for era < 518 in Kusama chain
• Tested a case where lastReward is available and it is null
• Updated the existing tests
• I did not test a case with a partially claimed era

Todos

• Minor adjustment for query param unclaimedOnly to work with the new statuses.
• Review all the latest changes from fix: claimed in staking info endpoint #1445 and make sure that is all implemented in this endpoint
• Test with validator and nominator accounts.
• Update docs.