When two borders overlap, they will automatically merge into a single,
clean border instead of overlapping.
This improves visual clarity and reduces rendering glitches around corners.
For example:
```
assert_eq!(Cell::new("┘").merge_symbol("┏", MergeStrategy::Exact).symbol(), "╆");
```
Co-authored-by: pauladam94 <poladam2002@gmail.com>
Co-authored-by: Paul Adam <65903440+pauladam94@users.noreply.github.com>
Co-authored-by: Orhun Parmaksız <orhunparmaksiz@gmail.com>
Co-authored-by: Orhun Parmaksız <orhun@archlinux.org>
Co-authored-by: Josh McKinney <joshka@users.noreply.github.com>
