Halve the number of calls to cosd, sind in spherical cellarea (#794)

ext/RastersProjExt/cellarea.jl

@@ -38,9 +38,11 @@ end
 
 _lonlat_to_sphericalpoint(args) = _lonlat_to_sphericalpoint(args...)
 function _lonlat_to_sphericalpoint(lon, lat)
-    x = cosd(lat) * cosd(lon)
-    y = cosd(lat) * sind(lon)
-    z = sind(lat)
+    lonsin, loncos = sincosd(lon)
+    latsin, latcos = sincosd(lat)
+    x = latcos * loncos
+    y = latcos * lonsin
+    z = latsin
     return SphericalPoint(x,y,z)
 end
 
@@ -182,4 +184,4 @@ function axis_is_degrees(crs::Proj.CRS, axis_index::Int; context::Ptr{Proj.PJ_CO
     # in which case we should technically return true.
     # We'd also have to return the conversion factor in this case, and maybe the category (radians or degrees)...
     return isequal(unit_str, "degree")
-end
+end