The new `--new` or `-n` flag allows to create a new revision after the
single revision being described.
Running `jj-cz --new` is the equivalent of running `jj-cz --new @`,
describing the current revision and creating a new revision after it.
Passing several revisions to `jj-cz` with the `--new` flag will result
in an error.
Allows to set the revision message of multiple revisions by passing
them as arguments. This only supports simple revisions, such as `@`,
`@-`, `xs`, and so on. Comple revisions such as `@..@-` are not
supported.
Fixes: #5
Replace CLI executor with jj-lib integration, implement full interactive
commit workflow via prompts, and add mock infrastructure for testing.
Add CLI integration tests and error handling tests.
phundrak
