Add OSC 8 link support to filepath in headers

[bemyak]

This PR adds OSC 8 support to difftastic. In practice, it means that links in hunk headers are now "clickable" inside some editors (Zed, VSCode, etc), and bring the user to the correct line in file.

Additional links:

• https://gist.github.com/egmontkob/eb114294efbcd5adb1944c9f3cb5feda
• https://github.com/Alhadis/OSC8-Adoption/

[bemyak]

Hmm, not sure why the test is failing. I updated the samples file, it has no changes when I run ./sample_files/compare_all.sh locally 🤔

[Wilfred]

Overall this looks great, and I'm not sure why the regression test is failing either.

I'm not sure whether the line number syntax is valid though. Testing on my personal linux laptop in the gnome terminal produces this when I click on a link:

Have you see this behaviour? I wonder how other tools with OSC URLs are handling this.

[bemyak]

Yeah, unfortunately line numbers specification is not in the standard, so it depends on the terminal emulator and the OS. I will switch back to slightly less supported, but much more safe # separator.

[Wilfred]

Testing in VS Code also seems to be looking for a file literally called foo.el:123 FWIW.

[Wilfred]

In practice, it means that links in hunk headers are not "clickable"

Do you mean that links are clickable?

[bemyak]

Testing in VS Code also seems to be looking for a file literally called foo.el:123 FWIW.

Could you pull the latest changes? It works for me:
Screencast_20260224_153947.webm

Do you mean that links are clickable?

I meant to spell "are now clickable", sorry.

[bemyak]

Did you have a chance to test it?