ENH: Implement rounding for floating dtype array #38844
Code proposed in the staled PR #38866

- [x] closes #38844
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [x] whatsnew entry

can you merge master Thanks for all your reviews! I will take time to implement them, but I can't before Saturday. I pushed some modifications:
- I added a small `test_function.py` in `tests/arrays/masked/`
- I merged the `_apply` and the `round` methods to have only the `round` method
- I merged master some precommit issues

```
Performing static analysis using mypy
pandas/core/arrays/numeric.py:241: error: "T" has no attribute "_data"  [attr-defined]
pandas/core/arrays/numeric.py:242: error: Too many arguments for "object"  [call-arg]
pandas/core/arrays/numeric.py:242: error: "T" has no attribute "_mask"  [attr-defined]
Found 3 errors in 1 file (checked 1242 source files)
``` @jreback two tests failed in code that I did not write/modify? Is this normal? thanks for merging master @benoit9126 this lgtm. thanks @benoit9126  Thanks a lot @benoit9126 !