fix(curses): show decimal latency scale

[Komzpa]

Summary

• format curses scale labels with decimal milliseconds when the scale is below 10 ms
• keep whole-millisecond labels for larger values so the existing scale stays compact
• add formatter coverage for sub-millisecond and fractional millisecond labels

Fixes #186.

Stacked on #636 because this reuses the new ui/format.c helper module from that PR.

Tests

• git diff --check
• make -j "$(nproc)" format-count-test && ./format-count-test
• make -j "$(nproc)"
• make check TESTS=format-count-test
• sudo python3 ./test/cmdparse.py
• GitHub compile-linux and lint passed