fix(refactor): Clean up handle_finalized_block and add E2E test coverage

[radhika-kapoor]

Closes #2697

###Summary
The handle_finalized_block function in the DKG manager actor was a single large function. This PR resolves refactoring the function and adding E2E test coverage.

###Solution

• Introduced FinalizedBlockContext struct -> groups the 7 individual arguments of handle_finalized_block into a single context struct, removing the clippy::too_many_arguments suppression and fulfilling the TODO comment.
• Extracted process_mid_epoch_block -> the mid-epoch path (reading dealer logs from block extra data, persisting them to the journal, clearing own log from state) is now a standalone method.
• Extracted resolve_epoch_outcome -> the boundary block path (reading the on-chain DKG outcome, computing local output, updating metrics, reading the validator contract) is now a standalone method.

###Tests Added
8 new E2E tests covering the per-block processing logic:

• mid_epoch_blocks_do_not_advance_epoch -> Epoch counter only advances on the last block of each epoch

• early_phase_dealer_distributes_shares -> Dealers distribute shares during the early phase

• midpoint_and_late_phase_dealer_finalization -> Dealers finalize state in midpoint and late phases

• restarted_node_ignores_prior_epoch_blocks -> Restarted node silently ignores blocks from prior epochs

• boundary_block_resolves_epoch_outcome_and_advances_state -> Boundary block resolves DKG outcome, advances epoch, populates next players, keeps group public key stable

• resolve_epoch_outcome_single_signer -> Same boundary block invariants with a single-signer setup

• dealer_log_in_block_extra_data_is_stored -> Dealer logs written into block extra data are stored and used to complete the ceremony

• own_dealer_log_in_block_is_cleared_from_state -> A dealer's own log is cleared from state after it appears in a finalized block