Add timestamp to the leak sensor data in DB, Fix to not escalate a minor leak if platform doesn't support it

[judyjoseph]

Description

Couple of enhancements/fixes in this PR

1. Add timestamp to the leak sensor data in DB

2. Fix to not escalate a minor leak if platform doesn't support it
   Fixes Bug: BMC leak escalation logic is not aligned with the HLD sonic-buildimage#28218

3. Also update the leak_severity in sensor table to in DB correctly as 'CRITICAL' 'MINOR' and 'None' strings

Motivation and Context

If the platform doesn't support escalation of a minor leak --> critical Skip it by checking the return value of platform API is 0
Add timestamp to sensor leak data entry in sensor table -- This will help triage when the leak started.

How Has This Been Tested?

Unit tests added which mock the leak conditions and test

Additional Information (Optional)

[Yakiv-Huryk]

LGTM.
@judyjoseph could you please also consider addressing the following in this PR?
sonic-net/sonic-mgmt#25769 (review)

[judyjoseph]

LGTM. @judyjoseph could you please also consider addressing the following in this PR? sonic-net/sonic-mgmt#25769 (review)

sure let me check @Yakiv-Huryk

[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[yxieca]

AI-assisted review — Approve

Reviewed the thermalctld leak-sensor changes:

• Escalation fix (if 0 < max_minor_secs < inf): a get_leak_max_minor_duration_sec() of 0/negative now correctly means "platform does not support time-based MINOR→CRITICAL escalation" instead of escalating immediately. Fixes sonic-buildimage#28218.
• leak_severity DB value now written as sensor_leak_severity.value ('MINOR'/'CRITICAL') with a 'None' fallback, instead of str(enum) which produced 'LeakSeverity.MINOR'. Applied consistently at all severity-write sites.
• timestamp added to the sensor-table write but deliberately excluded from the fvs_tuple diff-cache, so the advancing clock doesn't defeat change-detection and rewrite the row every poll.

Test coverage is solid — the no-escalation-when-duration-zero case, timestamp-on-transitions-only, and timestamp-not-in-diff-cache behaviors are all explicitly verified.

Looks good.

AI-assisted review, reviewed and approved by Ying Xie (@yxieca).

[mssonicbld]

Cherry-pick PR to msft-202608: Azure/sonic-platform-daemons.msft#73