TS-1740: Improve precision of stats values

Conversion between types, such as RecInt(int64_t) to RecFloat(float),
may lead to loss of precision.

In the old code, token value was defined with StatFloat type, it would casue
unnecessary conversion when type of token is not StatFloat.

it's best to keep value with the same type of token as much as possiable.

Signed-off-by: Yunkai Zhang <qiushu.zyk@taobao.com>
Signed-off-by: Zhao Yongming <ming.zym@gmail.com>