[BMC] Thermalctld hardening and fixes

[judyjoseph]

Description

Motivation and Context

This PR is for hardening thermalctld

1. In case there is a thermalctld restart preserve the escallation path logic, so that the leak sensors which had moved from Minor --> Critical won't be affected
2. Add a try-except condition for leak sensor update
3. Error log case when sensor goes faulty - place it int the persistent /host/event.log file
4. Error log case when a leak sensor tell it is leaking but Severity is None

How Has This Been Tested?

Added the following Unit tests

   1. test_restore_state_from_db - _restore_state_from_db rebuilds the escalation clock, latch, and last status from STATE_DB at startup.                                         ┃
   2. test_restart_latches_critical_even_if_platform_reads_minor - a restored CRITICAL stays CRITICAL after restart even if the platform now reads MINOR.                         ┃
   3. test_restart_resumes_minor_timer_and_escalates - a recorded MINOR whose window has elapsed escalates immediately after restart.                                             ┃
   4. test_restart_clears_when_sensor_reads_no_leak - restored state clears if the sensor now reads no leak.                                                                      ┃
   5. test_task_worker_survives_update_exception - a platform error in update() is caught so the monitoring thread stays alive and retries next cycle.                            ┃
   6. test_faulty_sensor_logged_to_event_log - a faulty leak sensor and its recovery are written to the durable event log.                                                        ┃
   7. test_leaking_without_severity_logs_event_error - a leaking healthy sensor reporting no severity logs an error to the event log.    

Additional Information (Optional)

[mssonicbld]

/azp run

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[mssonicbld]

This PR has backport request label(s) for branch(es): msft-202608, but is missing required test information. Please make sure you tick the tested branch(es) in the Tested branch section and provide test evidence (e.g., 202608: <test result>) in the Test result section as well in your PR description.

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[mssonicbld]

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[mssonicbld]

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