arrow-cast: decimal parsing tracking issue

I've noticed multiple issues related to parsing decimals in arrow-cast, so creating a central issue to track them together

- https://github.com/apache/arrow-rs/issues/5068
- https://github.com/apache/arrow-rs/issues/5762
- https://github.com/apache/arrow-rs/issues/9422
- https://github.com/apache/arrow-rs/issues/9170
- https://github.com/apache/arrow-rs/issues/9410
- https://github.com/apache/arrow-rs/issues/7355
- https://github.com/apache/arrow-rs/issues/10664
- https://github.com/apache/arrow-rs/issues/10665
- https://github.com/apache/arrow-rs/issues/10666
- https://github.com/apache/arrow-rs/issues/10795
- https://github.com/apache/arrow-rs/issues/10794
- https://github.com/apache/arrow-rs/issues/10793
- https://github.com/apache/arrow-rs/issues/10792
- https://github.com/apache/arrow-rs/issues/10791
- https://github.com/apache/arrow-rs/issues/10790
- https://github.com/apache/arrow-rs/issues/10789
- https://github.com/apache/arrow-rs/issues/10788
- https://github.com/apache/arrow-rs/issues/10787

Start by reviewing the linked arrow-rs issues, which document the separate decimal-parsing problems tracked here. This issue names no file, test, entry point, or acceptance criterion, so completion cannot be determined from the tracking text alone.

Written by the indexing model from the issue text.