Use u8 for Decimal Precision and Scale

[tustvold]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

The maximum precision and scale for decimal types is 76, and yet we consume an entire usize to store this information. This is most pronounced on BasicDecimal where the precision and scale take up more memory than the actual value data 😱

Describe the solution you'd like

I would like to propose using u8 for these instead of usize

Describe alternatives you've considered

Additional context

Thoughts @liukun4515

[liukun4515]

It's reasonable for me.
I think the data type of Decimal128(usize, usize), should be changed too

[psvri]

Hello,

I will pick this up if no one has started working on it.

[liukun4515]

It's reasonable for me. I think the data type of Decimal128(usize, usize), should be changed too

Do you have some comments about the data type of the decimal128?
FYI @psvri @tustvold

[psvri]

I have changed datatype to Decimal128(u8, u8) and Decimal256(u8, u8) .