validate steps and add pyproj to dependencies

Author: philipc2

pyproject.toml

@@ -44,6 +44,7 @@ dependencies = [
   "hvplot",
   "healpix",
   "polars",
+  "pyproj"
 ]
 # minimal dependencies end
 

uxarray/cross_sections/dataarray_accessor.py

@@ -80,6 +80,9 @@ def __call__(
         >>> uxda.cross_section(lon=0, steps=200)
         """
 
+        if steps < 2:
+            raise ValueError("steps must be at least 2")
+
         great_circle = start is not None or end is not None
         const_lon = lon is not None
         const_lat = lat is not None