have an arg-file mode to the CLI

often (we should be so lucky) one hits a limit of the arg length a program can test. The canonical solution to this is to pass a file and we read that and parse the args out of the file.

We could have `bosatsu file-command --input foo`.

One wild idea is that the format of the file should be a bosatsu file that evaluates to an expression of type `List[String]`, or even `List[List[String]]` which is interpreted many runs of the command.

Start by locating the Bosatsu CLI argument parser and reviewing how file-command currently receives arguments. Resolve whether --input should read one argument list or evaluate a Bosatsu expression producing List[String] or List[List[String]], then add coverage showing that the selected format avoids command-line length limits.

Written by the indexing model from the issue text.