Add Tensor(signed char)

Summary: The most popular trace (according to this dashboard: https://fburl.com/unidash/iv4evgh6) is currently unsupported by param trace because we get a key error when encountering the `Tensor(signed char)` type. This diff resolves this issue.

Reviewed By: bahlneeraj

Differential Revision: D56451067

fbshipit-source-id: a9ef08d7b73b665d7f6e2f4414aec961b9548589

train/comms/pt/commsTraceParser.py

@@ -23,6 +23,7 @@
     "Tensor(c10::Half)": "half",
     "Tensor(c10::BFloat16)": "bfloat16",
     "Tensor(unsigned char)": "char",
+    "Tensor(signed char)": "char",
 }