Re: [PATCH v5 1/1] cat-file: add mailmap subcommand to --batch-command

> git-cat-file(1)'s --batch-command works with the --use-mailmap option,
> but this option needs to be set when the process is created. This means
> we cannot change this option mid-operation.
>
> At GitLab, Gitaly keeps interacting with a long-lived git-cat-file
> process and it would be useful if --batch-command supported toggling
> mailmap dynamically on an existing process.
>
> Add a `mailmap` subcommand to --batch-command that takes a boolean
> argument (usual ways you can specify a boolean value like 'yes', 'true',
> etc., are supported). Mailmap data is loaded lazily and kept in memory,
> while a helper centralizes the one-time load path used both at startup
> and from the batch-command handler.
>
> Extend tests to cover runtime toggling, startup option interactions
> (`--mailmap`/`--no-mailmap`), accepted boolean forms, and invalid values.
>
> Signed-off-by: Siddharth Asthana <siddharthasthana31@gmail.com>
> ---
> CI: https://gitlab.com/gitlab-org/git/-/pipelines/2456596910