Add integrated GPS/NTP time sync

[hjoungjoo]

Summary

• add integrated Time Sync monitoring with GPS and NTP sources
• select the best available time source by estimated quality, with GPS/NTP-specific status
• add optional helper-mediated system clock and RTC sync requests
• add software PPS status, Time Sync UI, NTP server selection, and docs

Context

This is split out from the larger MF PiFinder compatibility branch as a focused draft PR. Time Sync is off by default; when enabled it can compare GPS and NTP, and it handles poor NTP/network conditions by reporting unavailable or low-quality NTP rather than blocking normal PiFinder operation.

Testing

• cd python && pytest tests/test_gps_time_sync.py tests/test_gps_time_sync_helper.py tests/test_gps_time_sync_status_ui.py tests/test_gps_time_sources.py -q
• python3 -m py_compile python/PiFinder/gps_time_sync.py python/PiFinder/gps_time_sync_helper.py python/PiFinder/gps_gpsd.py python/PiFinder/gps_ubx.py python/PiFinder/gps_ubx_parser.py python/PiFinder/main.py python/PiFinder/ui/callbacks.py python/PiFinder/ui/gps_time_sync_status.py python/PiFinder/ui/menu_structure.py python/PiFinder/ui/textentry.py
• git diff --check upstream/main...HEAD

Notes

• default remains disabled via time_sync_enabled=false
• NTP custom server entry is handled from the NTP Server > Custom item
• outdoor GPS validation is still planned, so this remains Draft

[brickbots]

Thank you @hjoungjoo for sharing this. This PR is interesting, and I do like the nerdiness of good time sync, but it adds 3,000+ lines of code and does not seem to improve the PiFinder user experience.

Aside from setting system time properly for non-networked PiFinders, what other benefits were you aiming for with this code?

[hjoungjoo]

Thank you @hjoungjoo for sharing this. This PR is interesting, and I do like the nerdiness of good time sync, but it adds 3,000+ lines of code and does not seem to improve the PiFinder user experience.

Aside from setting system time properly for non-networked PiFinders, what other benefits were you aiming for with this code?

Time synchronization is something I expect will be necessary for the features I have in mind, so I started working on it while adding GPS-related functionality.

This was done as a preparatory step because, when implementing guiding functionality for INDI mount control, accurate timing intervals and time calculations are needed in order to estimate the required movement amount and speed.

However, even though I have only implemented the basic framework so far, it has already caused changes in too many areas, so I am currently wondering whether I should revert it and start over.