0.9: O(1) queue-depth counts (getQueuedTaskCount/getProcessingTaskCount)

feat: add markTasksAsError for efficient bulk dead-load draining

Bulk sibling of markTaskAsError that snapshots ml_tasks once and uses a
targeted LREM per task instead of re-scanning the whole list per call, so a
maintenance sweep can drain thousands of leaked queue entries cheaply.
Skips the cancellation flag since callers use it for already-terminal tasks.

feat: add markTaskAsError to fail and drain a task from the queue

When an external system of record (webhook-server timeout sweep, frontend
/fetch give-up) marks a request errored, ModelQ must agree: drain the task
from ml_tasks/queued_requests/processing_tasks and write a terminal failed
state so no worker keeps (re)processing abandoned work. Closes the
queued_requests leak for error/timeout paths (previously only clean
completion removed the queue index).

feat: fully drain a task on removeTaskFromQueue (cancel)

removeTaskFromQueue() only dropped queued_requests when the task was still
present in ml_tasks. A cancelled/given-up task that had already left ml_tasks
stayed in the queued_requests index (inflating queue_num/queue_time) and in
processing_tasks. Now always zRem queued_requests + sRem processing_tasks so a
cancelled task is neither counted nor retried, regardless of where it sits.

fix stuck processing_tasks and queued_requests leak

Mirrors modelq python 1.0.11:
- worker_loop: persist startedAt on Task and status='processing'
  on task:{id} so storeFinalTaskState preserves them
- requeueStuckProcessingTasks: fall back to queued_at when
  started_at is missing (covers workers crashed in SADD→SET window)
- storeFinalTaskState: zRem queued_requests on terminal state

Merge pull request #1 from ModelsLab/fix-task-fetch

fix task details

fix data mapping for payload

fix

added workers