Implement unit tests for all existing yahcli command params

Now that the setup for unit testing in yahcli is finished and working, write unit tests for all params of each command. NOTE: this is an exercise of reinforcing current behavior, not of fixing bugs! If bugs are found with a param then please file a ticket with more details, but right now we are more concerned about getting tests written around the current functionality.

There are two test suites already written for the base `yahcli` command (i.e. params that apply to every yahcli command) and the system files command. Follow the examples of these unit tests, found in `YahcliCommandParamsTest` and `SysFilesCommandTest` respectively.

Since `main` isn't available, use the `20994-yahcli-param-unit-tests` branch as the base for all changes. For each new set of tests, create a separate branch so we can merge them to `main` when it's open again.