Add FilterRunOnce support (--no-run-once) to avoid duplicate GPO task runs

[Byxs20]

Summary

This PR adds FilterRunOnce support — an Item-Level Targeting filter that
ensures a Scheduled Task runs only once, preventing accidental repeated
execution across multiple GPO refresh cycles.

Problem

Without this filter, a GPO Scheduled Task re-executes on every Group Policy
refresh (default every 90 minutes on domain members). If the operator gets
pulled away or the task takes time to trigger, the command can run
multiple times — leaving unnecessary artifacts, creating duplicate accounts,
or triggering detection.

Solution

• Default behavior: run_once=True — the task self-deletes after first
  execution via <FilterRunOnce> in the ScheduledTasks XML.
• New CLI flag: --no-run-once disables this behavior, restoring the
  original "reapply on every refresh" behavior when intentionally needed.

Changes

File	Change
pygpoabuse/scheduledtask.py	Added run_once parameter to __init__; generates <FilterRunOnce> XML block
pygpoabuse/gpo.py	update_scheduled_task() now accepts and passes through run_once
pygpoabuse/cli.py	New --no-run-once argument; defaults to True

Example

By default the task runs once and stops:

python3 pygpoabuse.py DOMAIN/user:password -gpo-id -command "..."

To allow repeated execution on every GPO refresh:

python3 pygpoabuse.py DOMAIN/user:password -gpo-id -command "..." --no-run-once