RTC Failover to Monotonic Time Since Boot

[nateinaction]

Description

This PR introduces automatic failover in the RTC component to a monotonic time since boot if the RTC is unavailable.

Related Issues/Tickets

Resolves #110

How Has This Been Tested?

• Unit tests
• Integration tests
• Z Tests
• Manual testing (describe steps)

make test-integration
====================================================================== test session starts =======================================================================
platform darwin -- Python 3.13.5, pytest-8.3.3, pluggy-1.5.0
rootdir: /Users/nate/code/github.com/open-source-space-foundation/proves-core-reference
plugins: fprime-gds-4.0.2a9
collected 4 items                                                                                                                                                

FprimeZephyrReference/test/int/rtc_test.py ....                                                                                                            [100%]

======================================================================= 4 passed in 26.35s =======================================================================

Screenshots / Recordings (if applicable)

Checklist

• Written detailed sdd with requirements, channels, ports, commands, telemetry defined and correctly formatted and spelled
• Have written relevant integration tests and have documented them in the sdd
• Have done a code review with
• Have tested this PR on every supported board with correct board definitions

Further Notes / Considerations

[Mikefly123]

LGTM!