system/manager: atomic power_watchdog write + self-check verification (fixes #36680)

[Najib632]

Description

Fixes #36680

This PR addresses a race condition in system/manager/manager.py that caused unexpected device shutdowns.

The Issue:
Previously, manager.py updated the /var/tmp/power_watchdog file by opening it with w mode, which truncates the file to 0 bytes before writing the new timestamp. If the external AGNOS power monitoring process read the file during this brief window, it would see an empty file (interpreted as 0), assume the watchdog had expired, and trigger an immediate shutdown.

The Fix:
Implemented an atomic write pattern:

1. Write the new timestamp to a temporary file (/var/tmp/power_watchdog.tmp).
2. Use os.rename to atomically replace the target file.
   This guarantees that the reader process always sees a valid file content—either the old timestamp or the new one—but never an empty file.

Verification:

• Added a runtime self-verification step that reads the file back immediately after the update to ensure the timestamp is valid.
• If the verification fails (which should be impossible with os.rename), a critical error is logged to help with future debugging.

[greatgitsby]

this PR makes a ton of unnecessary changes that bloat the diff

[Najib632]

this PR makes a ton of unnecessary changes that bloat the diff

Thank you sir, I have removed the unnecessary changes I made

[greatgitsby]

i meant primarily on reorganizing imports and indents

[Najib632]

i meant primarily on reorganizing imports and indents

Okay sir, I switched the HEAD back to a previous commit that didn't have the bloat and then applied the changes from there

[Bglg2k]

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[adeebshihadeh]

Still way too complicated, see how I did it here: 436e3de

[Najib632]

Still way too complicated, see how I did it here: 436e3de

That was neat sir, adding it to the atomic_write really made it simpler.