[Feat]: Add option to `om ci` for selective package builds

### **Description** Currently, `om ci` builds **all packages** defined in the flake output. It would be very useful to have an option to build only specific packages or exclude certain ones. --- ### **Proposed Feature** Add support for: * `--build .#a .#b .#c` – Only builds the specified packages. * `--exclude-build .#a .#b` – Builds everything except the excluded packages. --- ### **Use Case** Example scenario: * I have an editor configuration with three packages: `bare`, `core`, and `full`. * The `full` package includes large dependencies (e.g., TeX packages) that I don’t want to build in CI. * Similarly, sometimes building Docker images should be skipped in CI to save time and resources.