Implements 5 new C functions requested by the Craft (Astrolock) API team:
- tle_from_lines(text, text): two-argument TLE constructor
- observer_from_geodetic(float8, float8, float8): numeric observer constructor
- observe(tle, observer, timestamptz): single-call propagate + topocentric
- sgp4_propagate_safe(tle, timestamptz): returns NULL on propagation error
- observe_safe(tle, observer, timestamptz): returns NULL on propagation error
Refactors do_propagate() into safe/unsafe variants to support NULL returns.
Adds regression test (convenience.sql) covering all new functions including
an equivalence test verifying observe() matches the manual two-step pipeline.
All 6 regression tests pass.
6 custom types (tle, eci_position, geodetic, topocentric, observer,
pass_event), 67 SQL functions, 2 operators (&&, <->), and a GiST
operator class for altitude-band indexing. Wraps Bill Gray's sat_code
for SGP4/SDP4 propagation with WGS-72 constants for propagation and
WGS-84 for coordinate output. All 5 regression tests pass on PG 18.
