Add creation of epoch_year and epoch_day variables when initialized from satrec

[interplanetarychris]

The value exists when created from a TLE, but not when created from an SGP4 satrec.

https://github.com/consensys-space/trusat-orbit/blob/00bf2f2a9f674e03e4b01fbc73fb1bb48e6df494/tle_util.py#L422