[Feature Request] himl cli - deep filter

Consider the following `.yaml` file.

examples/simple/default.yaml
```
deep:
key1: v1
key2: v2
deep_list:
- item1
- item2
```
## Request
A feature to filter deep keys like, `deep.key1`, `deep.key2`. Currently, the cli supports only top-level keys to filter. (ie, `deep` and ` deep_list` in the example)

Start with examples/simple/default.yaml and the CLI's existing top-level filtering behavior. Trace how keys such as deep and deep_list are selected, then define and verify filtering for paths such as deep.key1 and deep.key2 with nested YAML data.

Written by the indexing model from the issue text.