Remove obsolete Commit and Finalize tasks from the committor service

[snawaz]

Outcome

Remove the obsolete separate Commit and Finalize tasks from the committor service after commit paths converge on CommitFinalize*. Reduce the task API and duplicated code while preserving commit behavior.

Scope

The migration in #1739 makes the old task variants, their preparation branches, and separate-finalization recovery code unnecessary. The remaining builders also duplicate construction of the same combined tasks.

• Remove CommitTask, FinalizeTask, their enum variants, and the constructors, budgets, metrics, and recovery branches used only by them.
• Keep shared state/diff and inline/buffer delivery support with the combined tasks.
• Consolidate duplicate commit builders and remove unused task types, traits, helpers, and legacy test adapters.
• Update fixtures to use combined tasks and retain coverage for buffer preparation, cleanup, nonce handling, and action ordering.
• Preserve public intent semantics, authority checks, callbacks, bundle atomicity, and persisted status formats.

Standalone undelegation and multiple-transaction execution remain necessary for ownership return and transaction limits. Simplifying the single/two-stage executors is a follow-up.

PR: #1764.