Improve handling of split multibyte characters in display

[CathalMullan]

Could probably do some graphemes logic to make this work as-is, but would rather not.

Instead of guessing the length of characters, we can start the next branch at the start of the text.

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #158 will not alter performance

_{Comparing 157-improve-handling-of-multi-byte-characters-in-router-display (791a132) with main (60b37bc)}

Summary

✅ 16 untouched benchmarks

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

:white_check_mark: All tests successful. No failed tests found.

Files with missing lines	Coverage Δ
src/node/display.rs	88.00% <100.00%> (+1.20%)	:arrow_up: