Fix: Obelisk TimestampPrecision as string

When passing a TimestampPrecision object into the params,
the full name of the enum gets encoded into
TimestampPrecision.MILLISECONDS e.g.

Obelisk understandably throws a fit and desires no prefixes.
We missed a `.value` call, added back here.

Author: Epse

src/obelisk/asynchronous/producer.py

@@ -41,7 +41,7 @@ async def send(self, dataset: str, data: List[dict],
 
         params = {
             'datasetId': dataset,
-            'timestampPrecision': precision,
+            'timestampPrecision': precision.value,
             'mode': mode.value
         }