feat: add git checkout support

[kenwoodjw]

Summary

Closed #1728

• Add compact rtk git checkout support for branch switching, new/reset branch checkout, and path restore forms.
• Enable hook rewrite coverage for git checkout ....
• Preserve checkout exit codes while surfacing concise ok ... success output and focused failure messages.

Test plan

• cargo fmt --all && cargo clippy --all-targets && cargo test
• Manual testing: rtk <command> output inspected

  cargo build

  tmp=$(mktemp -d)
  cd "$tmp"
  git init -q -b main
  git config user.email t@t.t
  git config user.name t
  git commit -q --allow-empty -m init

  /path/to/rtk/target/debug/rtk git checkout -b feature/test
  # expect: ok feature/test (new)

  /path/to/rtk/target/debug/rtk git checkout main
  # expect: ok main

  check path restore：

  printf 'original\n' > a.txt
  printf 'original\n' > b.txt
  git add a.txt b.txt
  git commit -q -m 'add files'

  printf 'changed\n' > a.txt
  printf 'changed\n' > b.txt

  /path/to/rtk/target/debug/rtk git checkout HEAD -- a.txt b.txt
  # expect: ok 2 files restored

Important: All PRs must target the develop branch (not master).
See CONTRIBUTING.md for details.

[CLAassistant]

All committers have signed the CLA.

[aeppling]

Hey @kenwoodjw

Thanks for this addition,
Here is some things to be addressed before merge.

Use the shared runner

run_checkout hand-rolls exec_capture + manual print/track like the legacy run_add/run_fetch. It fits runner::run_filtered_with_exit + RunOptions::with_tee(...) (output is a pure function of args, raw, exit).
That gives the never_worse guard, tee reversibility, and central tracking for free.

Failure filter drops the filenames

On a dirty tree, it keeps the error: header and Aborting but discards the indented file list, leaving "the following files" with no files.

[aeppling]

@kenwoodjw got a failing test :p

[kenwoodjw]

@kenwoodjw got a failing test :p

fixed, Please try again. Thanks.

[aeppling]

Hey @kenwoodjw

LGTM, thanks for contributing to RTK by adding more coverage :)