Add ability to inspect specific commits and diffs via command line arguments

**Is your feature request related to a problem? Please describe.**

It should be easily possible to inspect the changes by a given git commit/patch or range of commits.

**Describe the solution you'd like**

There should be command line arguments to show the git commits.

*Examples:*
```shell
# inspect a specific git commit
gitui --commit COMMITHASH

# inspect a range of commits
gitui --commit REV1..REV2

# inspect a range of commits and skip the first one
gitui --commit REV1^..REV2

# inspect from a given commit to HEAD
gitui --commit REV1..HEAD
gitui --commit REV1..

# inspect a git patch file
gitui --inspect SOMEFILENAME.patch
```

**Describe alternatives you've considered**

There should be a method via the CLI UI for selecting a range of commits or a patch file for inspection.

**Additional context**

- See [Git Revision](https://git-scm.com/docs/gitrevisions) on how a range of git commits can be specified
- See [Git Diff and Patch](https://www.freecodecamp.org/news/git-diff-and-patch/) and [Git Format-Patch](https://git-scm.com/docs/git-format-patch) on details of git patch files

まず、gitui のコマンドライン引数の解析処理と、既存の commit または diff の検査用エントリーポイントを見つけます。--commit と --inspect を使用する例が、Git のリビジョン範囲とパッチファイルにどのように対応すべきかを確認します。指定された commit、範囲、HEAD、パッチファイルの各ケースで、要求された引数が機能すれば完了です。

索引モデルが issue の本文から書いたものです。