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.
