feat: add precUint

[quagmt]

Description

• Add PrecUint method which returns precision as uint8. This function can be useful when combining with other functions like Round or Trunc as they accept uint8 as input
• Example:

oneUnit := udecimal.MustParse("0.001")
a := udecimal.MustParse("1.123456")
b := a.Trunc(oneUnit.PrecUint()) // b = 1.123

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.55%. Comparing base (603c3aa) to head (a0189ad). Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #13 +/- ## ======================================= Coverage 94.54% 94.55% ======================================= Files 5 5 Lines 1265 1267 +2 ======================================= + Hits 1196 1198 +2 Misses 37 37 Partials 32 32 ```

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