To represent KiCad's internal units (1 nm), it's enough to have:
- 6 decimal digits in mm;
- 8 decimal digits in inches.
There's not much point in reducing the precision.
Up to 10 digits allowed just in case.
Also changes precision to 6 decimal digits by default.
IPC2581 is a modern production file exchange system. It provides
single-file data output for an entire board including BOM and netlist
information.
Fixes https://gitlab.com/kicad/code/kicad/-/issues/1954