Allow reading walltime variables

- The variables are slightly different in each processor
- This causes issues with xarray concatenation.
- Read proc 0 variables and discard the rest
- (Wtime stats should be the nearly the same for all procs)
- Also saves other variables which are part of
_BOUT_PER_PROC_VARIABLES

xbout/load.py

@@ -972,7 +972,11 @@ def _trim(ds, *, guards, keep_boundaries, nxpe, nype, is_restart):
         ):
             trimmed_ds = trimmed_ds.drop_vars(name)
 
-    to_drop = _BOUT_PER_PROC_VARIABLES
+    if ds["MYPE"] == 0:
+        # Keep per-process variables from the root process
+        to_drop = None
+    else:
+        to_drop = _BOUT_PER_PROC_VARIABLES
 
     return trimmed_ds.drop_vars(to_drop, errors="ignore")