Use less SPICE functions

[hyrodium]

This line

AsteroidThermoPhysicalModels.jl/test/TPM_Ryugu.jl

Line 42 in b7cd460

P = SPICE.convrt(7.63262, "hours", "seconds") # Rotation period of Ryugu

can be replaced with Unitful features.

julia> using SPICE, Unitful

julia> P = SPICE.convrt(7.63262, "hours", "seconds")
27477.432

julia> uconvert(u"s", 7.63262u"hr")
27477.432 s

julia> convert(Float64, (7.63262u"hr") / (1u"s"))
27477.432