Tweaked script field arg parsing to strip whitespace almost everywhere

The whitespace sensitivity of field args was starting to be a problem,
mostly for advanced plotmpl.py usage (which tbf might be appropriately
described as "super hacky" in how it uses CLI parameters):

  ./scripts/plotmpl.py \
      -Dcase=" \
          bench_rbyd_attr_append, \
          bench_rbyd_attr_remove, \
          bench_rbyd_attr_fetch, \
          ..."

This may present problems when parsing CSV files with whitespace, in
theory, maybe. But given the scope of these scripts for littlefs...
just don't do that. Thanks.

scripts/plot.py

@@ -1423,14 +1423,20 @@ if __name__ == "__main__":
         '-b', '--by',
         action='append',
         type=lambda x: (
-            lambda k,v=None: (k, v.split(',') if v is not None else ())
+            lambda k, vs=None: (
+                k.strip(),
+                tuple(v.strip() for v in vs.split(','))
+                    if vs is not None else ())
             )(*x.split('=', 1)),
         help="Group by this field. Can rename fields with new_name=old_name.")
     parser.add_argument(
         '-x',
         action='append',
         type=lambda x: (
-            lambda k,v=None: (k, v.split(',') if v is not None else ())
+            lambda k, vs=None: (
+                k.strip(),
+                tuple(v.strip() for v in vs.split(','))
+                    if vs is not None else ())
             )(*x.split('=', 1)),
         help="Field to use for the x-axis. Can rename fields with "
             "new_name=old_name.")
@@ -1438,13 +1444,20 @@ if __name__ == "__main__":
         '-y',
         action='append',
         type=lambda x: (
-            lambda k,v=None: (k, v.split(',') if v is not None else ())
+            lambda k, vs=None: (
+                k.strip(),
+                tuple(v.strip() for v in vs.split(','))
+                    if vs is not None else ())
             )(*x.split('=', 1)),
         help="Field to use for the y-axis. Can rename fields with "
             "new_name=old_name.")
     parser.add_argument(
         '-D', '--define',
-        type=lambda x: (lambda k,v: (k, set(v.split(','))))(*x.split('=', 1)),
+        type=lambda x: (
+            lambda k, vs: (
+                k.strip(),
+                {v.strip() for v in vs.split(',')})
+            )(*x.split('=', 1)),
         action='append',
         help="Only include results where this field is this value. May include "
             "comma-separated options.")