Add update property to TransactionEvent (#72)

* Add update property to TransactionEvent

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

python/pycrdt/_pycrdt.pyi

@@ -58,6 +58,10 @@ class TransactionEvent:
     """Event generated by `Doc.observe` method. Emitted during transaction commit
     phase."""
 
+    @property
+    def update(self) -> bytes:
+        """The emitted binary update"""
+
 class SubdocsEvent:
     """Event generated by `Doc.observe_subdocs` method. Emitted during transaction commit
     phase."""