CLN: remove unnecessary float64 cast in _dt_total_seconds

PyArrow automatically promotes int64 to double when multiplying with float.

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Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: fangchenli

pandas/core/arrays/arrow/array.py

@@ -2916,12 +2916,10 @@ def _dt_to_pytimedelta(self) -> np.ndarray:
 
     def _dt_total_seconds(self) -> Self:
         # Convert duration to seconds using PyArrow compute
-        # Must cast to int64 first since duration -> float64 is not supported
         unit = self._pa_array.type.unit
         unit_to_seconds = {"s": 1.0, "ms": 1e-3, "us": 1e-6, "ns": 1e-9}
         factor = unit_to_seconds[unit]
-        float_arr = pc.cast(pc.cast(self._pa_array, pa.int64()), pa.float64())
-        result = pc.multiply(float_arr, factor)
+        result = pc.multiply(pc.cast(self._pa_array, pa.int64()), factor)
         return self._from_pyarrow_array(result)
 
     def _dt_as_unit(self, unit: str) -> Self: