use half/bf16 lm_head output

[irexyc]

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[lzhangzz]

Do we still need the float instantiation for sampling kernels?

[irexyc]

Do we still need the float instantiation for sampling kernels?

some tests in tests/csrc/unittests use float inputs.

[lzhangzz]

Use the macro ENABLE_FP32 to skip the tests. We are not increasing the binary size for testing unused kernels. Or better, modify the tests to support half/bf16 data type.

[irexyc]

After removing the fp32 compilation option, the size is reduced by about 2MB.

To reduce the size, maybe we can use TORCH_LIBRARY to replace pybind11 and enable py-limited-api. If it works, there is no need to compile multiple versions of Python packages any more.

[lvhan028]

is TORCH_LIBRARY highly related to torch version?