ENH: handle unicode enc error in file_write()

One some (HPC) systems, we occasionally see random errors of the form

        UnicodeEncodeError: 'ascii' codec can't encode characters
        in position 4475-4476

when calling file_write() caused by run(..., capture_logs="file"). This may be
caused by oldish file systems that can't handle unicode files.

src/psweep/psweep.py

@@ -124,7 +124,10 @@ def flatten(seq):
 def file_write(fn: str, txt: str, mode="w"):
     makedirs(os.path.dirname(fn))
     with open(fn, mode=mode) as fd:
-        fd.write(txt)
+        try:
+            fd.write(txt)
+        except UnicodeEncodeError:
+            fd.write(txt.encode("ascii", errors="xmlcharrefreplace").decode())
 
 
 def file_read(fn: str):