This enables git.Command's Run to optionally use the given context directly so its deadline will be respected. Otherwise, it falls back to the previous behavior of using the supplied timeout or a default timeout value of 360 seconds.

repo's serviceRPC() calls now use the context's deadline (which is unset/unlimited) instead of the default 6-minute timeout. This means that large repo clones will no longer arbitrarily time out on the upload-pack step, and pushes can take longer than 6 minutes on the receive-pack step.

Fixes go-gitea#20680