feat!: internally compute indexes at match time (removes get/set_index)

[LoricAndre]

Checklist

• The title of my PR follows conventional commits
• I have updated the documentation (README.md, comments, src/manpage.rs and/or src/options.rs if applicable)
• I have added unit tests
• I have added integration tests
• I have linked all related issues or PRs

Description of the changes

Note: codecov runs on the PR on this repo, but feel free to ignore it.

[codecov]

Codecov Report

❌ Patch coverage is 56.00000% with 55 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/tui/event.rs	0.00%	19 Missing ⚠️
src/tui/app.rs	61.53%	7 Missing and 3 partials ⚠️
src/tmux.rs	22.22%	7 Missing ⚠️
src/helper/item.rs	0.00%	6 Missing ⚠️
src/tui/item_list.rs	53.84%	6 Missing ⚠️
src/item.rs	57.14%	3 Missing ⚠️
src/engine/fuzzy.rs	50.00%	1 Missing ⚠️
src/skim.rs	0.00%	1 Missing ⚠️
src/skim_item.rs	0.00%	1 Missing ⚠️
src/util.rs	96.66%	1 Missing ⚠️

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