Hotfix/search overlay move to end of line

[kenchou]

• Fix crash when jumping to the end of the line.
• add some unit tests for LineEditBuffer

see https://github.com/wez/wezterm/pull/5564#discussion_r1640757300 PR #5416

@wez @Mrreadiness

[kenchou]

Run nix build ./nix
  nix build ./nix
  shell: /usr/bin/bash -e {0}
  env:
    DETERMINATE_NIX_KVM: 1
    MAGIC_NIX_CACHE_DAEMONDIR: /home/runner/work/_temp/magic-nix-cache-dacd5adc-291f-4b75-b1db-d27b122d7034
warning: error: unable to download 'http://127.0.0.1:37515/na7sykizsgkzh9i3wc8m8pz5xfqib2rv.narinfo': HTTP error 429

       response body:

       GitHub API error: API error (429 Too Many Requests): StructuredApiError { message: "Request was blocked due to exceeding usage of resource 'Count' in namespace ''." }; retrying in 288 ms
disabling binary cache 'http://127.0.0.1:37515/' for 60 seconds
error: unable to download 'http://127.0.0.1:37515/na7sykizsgkzh9i3wc8m8pz5xfqib2rv.narinfo': HTTP error 418

       response body:

       GitHub API error: GitHub Actions Cache throttled Magic Nix Cache. Not trying to use it again on this run.
copying path '/nix/store/rbqg72wrmkzb0jk1hxcsm0lzkpva3dqf-source' from 'https://cache.nixos.org/'...

It seems to be a CI issue, please try again. @wez