Use more const functions.

[HaoYang670]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
As the const fn related features have been stabilized in rust 1.61: rust-lang/rust#93827, we could use more const functions in our code, such as the OffsetSizeTrait and some functions in Decimal.

Describe the solution you'd like
More constant folding is great!

Describe alternatives you've considered
We could not do this.

Additional context
(https://blog.rust-lang.org/2022/05/19/Rust-1.61.0.html#more-capabilities-for-const-fn)