Validate OMM reference context before propagation

[sylvesterkaczmarek]

Summary

Reject OMM metadata that is incompatible with the reference context assumed by dSGP4 propagation.

Changes

• require CENTER_NAME to resolve to EARTH
• require REF_FRAME to resolve to TEME
• require TIME_SYSTEM to resolve to UTC
• preserve the existing supported defaults when those optional fields are absent
• accept case-insensitive equivalents
• add regression tests for invalid, case-insensitive, and missing reference-context fields

Rationale

load_from_omm() previously accepted incompatible reference metadata and then propagated the elements using the Earth/TEME/UTC assumptions used internally by dSGP4. This change rejects those mismatches before propagation.

Validation

Focused regression validation passes. The upstream GitHub Actions workflow is currently waiting for maintainer approval to run for this fork PR.

[Sceki]

Hi @sylvesterkaczmarek ,

can you provide an actual input/use case where dSGP4 currently produces an incorrect or misleading result because of this?

[sylvesterkaczmarek]

Yes. A concrete case is an OMM with the normal SGP4 elements but REF_FRAME=EME2000.

Today load_from_omm() accepts it and produces the same propagatable object as if REF_FRAME=TEME, because the reference-frame metadata is not used when converting the OMM fields into the SGP4/TLE representation.

The caller therefore gets a propagated result without any indication that EME2000 elements were interpreted under dSGP4's TEME assumptions. The same issue applies to a non-UTC TIME_SYSTEM or non-Earth CENTER_NAME.

The purpose of this PR is to fail explicitly at ingestion rather than silently reinterpret incompatible metadata.