Port the guarded NMEA buffer, validated RMC clock samples and coordinate bounds from meshcore-dev/MeshCore#3624, #3625 and #3626. Adapt clock admission to retain this branch's signed date limits, bounded loop work, tracker acquisitions, sample consumption, diagnostics and periodic settings. Upstream-PR: https://github.com/meshcore-dev/MeshCore/pull/3624 Upstream-Commit: 1ac389bbef0084623a3115c526156ae8f414d3ea Upstream-PR: https://github.com/meshcore-dev/MeshCore/pull/3625 Upstream-Commit: 72ed4dcf08869c6900ef579e7af1b28471a86895 Upstream-PR: https://github.com/meshcore-dev/MeshCore/pull/3626 Upstream-Commit: 499727a71c564a7b5d451b8f480d940e185fe742 Co-authored-by: nullrouten0 <201262769+nullrouten0@users.noreply.github.com>