This PR refactors test_delegation to align with the new build Method

[OlufemiAdeOlusile]

This PR simplifies and unifies the delegation transaction handling by removing redundant use_build_cmd branches and consolidating transaction creation into a single clusterlib_utils.build_and_submit_tx flow.

Key Changes

• delegate_stake_addr

  • Removed conditional handling of use_build_cmd vs. send_tx.
  • Replaced both with clusterlib_utils.build_and_submit_tx for consistency.
  • Ensures returned DelegationOut uses tx_output instead of mixed outputs.
  • Balance validation updated to reference unified transaction output.

• test_delegation.py

  • Updated delegation tests (delegate using pool_id, delegate using vkey, delegation + deregistration, unknown addr, deregistered addr) to use build_method instead of use_build_cmd.
  • Simplified test logic by removing duplicated transaction signing/submission branches.
  • Maintained existing assertions on balance updates, stake key deposits, and delegation error handling.

  Regression RUN: https://github.com/IntersectMBO/cardano-node-tests/actions/runs/17407105869/job/49414294045

[mkoura]

Please also check for blockers from common.match_blocker, if using transaction build.

[OlufemiAdeOlusile]

addressed