fix: Update time handling to use TimeUtil for current time retrieval

[Chrisliao0806]

Description

This PR standardizes all time-related operations to use the custom TimeUtil utility class and ensures all task sensors use the poke mode for consistency.
Problem: The codebase had inconsistent time handling — some places used Python's built-in datetime.datetime.now() while others used TimeUtil. This made the code harder to maintain and potentially introduced timezone inconsistencies. Additionally, the new uptime validation sensors were using mode="reschedule" instead of the team's standard mode="poke".

Technical Implementation

1. Extended TimeUtil with now() method:
   • Added TimeUtil.now() class method that returns the current UTC time as a TimeUtil instance
   • This provides a single, consistent way to get the current time across the codebase
2. Standardized time operations in jobset_util.py:
   • Removed import datetime module, replaced with direct from datetime import timedelta
   • Converted all datetime.datetime.now() calls to TimeUtil.now()
   • Simplified time difference comparison from:

   now.to_datetime() - start_time.to_datetime() >= timedelta(seconds=wait_time_seconds)
   

   to:

   (now.time - start_time.time) >= wait_time_seconds
   

   • Fixed incorrect function call: changed query_time_series to list_time_series (the parameters being passed matched list_time_series signature, not query_time_series
3. Standardized sensor modes:
   • Changed wait_for_jobset_uptime_data from mode="reschedule" to mode="poke"
   • Changed ensure_no_jobset_uptime_data from mode="reschedule" to mode="poke"
4. Updated jobset_uptime_validation.py:
   • Simplified get_current_time() task to use TimeUtil.now() directly

Test

• GCP Composer name: chris-test (under GCP project: cienet-cmcs)
• GCP Composer version: 2.13.1
• test result: https://3450723b279f4f47af5e5f22135026a7-dot-us-central1.composer.googleusercontent.com/dags/jobset_uptime_validation/grid?dag_run_id=manual__2026-02-24T02%3A39%3A59.005105%2B00%3A00&task_id=v6e.ensure_no_jobset_uptime_data&tab=logs

Checklist

Before submitting this PR, please make sure (put X in square brackets):

• I have performed a self-review of my code.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have run one-shot tests and provided workload links above if applicable.
• I have made or will make corresponding changes to the doc if needed.