Clean up CeleryExecutor to use workload terminology and typing

[SameerMesiah97]

Description

This PR is a follow-up for PR #61153. It performs a non-functional cleanup of the Celery executor to better align it with the workload-based execution model being introduced in Airflow 3.2.

The changes include:

• Renaming task-centric methods and variables to use workload-oriented terminology where appropriate.
• Updating type annotations to consistently use workload abstractions (e.g. WorkloadKey, WorkloadInCelery, workloads.All).
• Improving docstrings and inline comments to reflect workload-based semantics.
• Minor naming improvements to reduce ambiguity.
• Adding missing periods to, fixing capitilization in, and rephrasing docstrings and comments where needed.

Method renames were applied selectively:

• Internal helper methods and non-public interfaces were updated to reflect workload terminology
• Methods closely tied to Celery internals or mirroring BaseExecutor / scheduler-invoked interfaces were left unchanged to preserve compatibility

No behavioral or functional changes are introduced.

Rationale

The Celery executor already supports workload-based execution, but parts of the implementation still reflect legacy task-centric terminology. This PR standardizes naming, typing, and documentation to improve consistency and readability.

• Method names were updated where safe (i.e. internal helpers not part of public or inherited interfaces). Methods that mirror BaseExecutor, are invoked by the scheduler, or are tightly coupled to Celery internals were intentionally left unchanged to avoid breaking contracts.

• Variables were renamed from “task” to “workload” where they represent Airflow execution units. Fields inherited from BaseExecutor (e.g. queued_tasks) and Celery-specific concepts (e.g. task_id) were preserved to maintain compatibility and clarity.

• Docstrings and comments were updated to consistently describe workloads while still distinguishing between Airflow workloads and Celery tasks where necessary.

• Typing was improved by preferring workload-based types while retaining legacy aliases required for compatibility across Airflow versions.

Notes

• The CeleryKubernetesExecutor has not been altered (save for a type: ignore to satisfy mypy) in this PR as it is now deprecated according to Issue Executor Callback support #62887

• Metrics (Stats.incr) and configuration paths were intentionally left unchanged, as they form part of Airflow’s external/operational interface (e.g. dashboards, alerts, and user configs). Renaming these could introduce unintended breaking changes or disrupt existing observability. This change is therefore scoped to internal naming, typing, and documentation updates only, without altering behavior or externally visible contracts.

Related

• PR Executor Synchronous callback workload #61153
• Issue Executor Callback support #62887