[Feature] Add fractional inches format

[Miki-AG]

Initial checklist

• Is this really a problem?
• I have searched the Github Issues for similar issues, but did not find anything.

Problem

Univer currently supports decimal-based measurement formats, but many industries—especially engineering, woodworking, and manufacturing—rely on fractional inches (e.g., 1/2", 5/16", 3/4") for measurements. Adding native support for fractional inch formatting (as MS Excel does) would improve usability and eliminate the need for workarounds.