Access dict keys and values

My script returns a dictionary from command `script.py command`. That works well. But when I try to list just keys (`script.py command keys`) or values (`script.py command values`), I get error `Cannot find target in dict` instead of the expected list of keys or values. Please extend `dict` handling with support for `.keys()` and `.values()` methods.

Reproduce the behavior with the mentioned script.py command, then trace Python Fire's dictionary target handling and the command entry point. Verify how keys and values are currently resolved, and consider the work complete when `script.py command keys` and `script.py command values` return the corresponding lists without the target error.

由索引模型根據 Issue 內容生成。