refactor(expr): drop redundant bytes(...) wrap in to_bytes

`PyExpr::to_bytes` returns `Bound<PyBytes>`, which crosses the FFI
boundary as Python `bytes`. The defensive `bytes(...)` wrap was a
no-op.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: timsaucer

python/datafusion/expr.py

@@ -446,7 +446,7 @@ def to_bytes(self, ctx: SessionContext | None = None) -> bytes:
         :doc:`/user-guide/io/distributing_work`.
         """
         ctx_arg = ctx.ctx if ctx is not None else None
-        return bytes(self.expr.to_bytes(ctx_arg))
+        return self.expr.to_bytes(ctx_arg)
 
     @classmethod
     def from_bytes(cls, buf: bytes, ctx: SessionContext | None = None) -> Expr: