feat(earthadmittance): add base earth admittance implementation

Author: amaurigmartins

src/engine/earthadmittance/base.jl

@@ -0,0 +1,7 @@
+@inline function Base.getproperty(f::Homogeneous, name::Symbol)
+	if name === :s || name === :t || name === :Γx || name === :γ1 || name === :γ2 ||
+	   name === :μ2
+		return getproperty(from_kernel(f), name)
+	end
+	return getfield(f, name)  # subtype-specific fields (if any)
+end