REF: use dict comprehension instead of map to process PROJ strings

pyproj/crs/crs.py

@@ -573,7 +573,11 @@ def to_dict(self) -> dict:
 
         """
 
-        def parse(val):
+        proj_string = self.to_proj4()
+        if proj_string is None:
+            return {}
+
+        def _parse(val):
             if val.lower() == "true":
                 return True
             if val.lower() == "false":
@@ -588,16 +592,13 @@ def parse(val):
                 pass
             return _try_list_if_string(val)
 
-        proj_string = self.to_proj4()
-        if proj_string is None:
-            return {}
-
-        items = map(
-            lambda kv: len(kv) == 2 and (kv[0], parse(kv[1])) or (kv[0], None),
-            (part.lstrip("+").split("=", 1) for part in proj_string.strip().split()),
-        )
+        def _process_step(step):
+            step_parts = step.lstrip("+").split("=", maxsplit=1)
+            if len(step_parts) == 2:
+                return step_parts[0], _parse(step_parts[1])
+            return step_parts[0], None
 
-        return {key: value for key, value in items if value is not False}
+        return dict(_process_step(step) for step in proj_string.strip().split())
 
     def to_cf(
         self,