Pow operator complex32 type UT failure on Windows

[Kanya-Mo]

🐛 Describe the bug

(Windows only) Pow operator gives incorrect result in UT test_binary_ufuncs_xpu.py::TestBinaryUfuncsXPU::test_pow_xpu_float16.
#798 is to fix this failure. However, additional overhead was introduced in type cast so we need to record this.

The failure is related to the cast of complex half type in kernel. If we convert with opmath_t{}, other ops like log will also gives incorrect results.

Versions

torch-xpu-ops: 47cbc58
pytorch: c8626a4e1f0553c8a9af32515555409d151a00c0