Make circup frozen library aware

Feature request.

When using circup to install a library, it also installs all of the dependencies. That is usually the correct thing to do, but when those dependencies are frozen, it wastes space.
suggestion: add a flag, or make it the default, to exclude frozen dependencies during installs. They should be shown as already installed.

Variation. If installing with --py, frozen library dependencies might be desired.
suggestion: add a flag to install frozen dependencies when --py is used.
suggestion: when installing source (--py) for frozen libraries have a flag to override the target folder. Putting them in the root folder instead of lib would let them be found before the frozen version.
Putting them in a user specified folder would allow access control by manipulating sys.path. Something like '/debug', '/unfrozen', or '/thawed'.

Some extra documentation (circup --help) about interaction with frozen libraries could be a good idea.

- List the steps to reproduce the problem below (if possible attach code or commands
to run): **LIST REPRO STEPS BELOW**

On discord in help-with-circuitpython
https://discord.com/channels/327254708534116352/537365702651150357/1248796673115816078

This arose when using
```bash
circup install --py adafruit_pyportal
```
then trying to add debug prints to the imported dependence libraries. Some worked, some didn't because they were frozen, but there was no indication that was the problem.

Start with the `circup install --py adafruit_pyportal` command and the `circup --help` output, then trace how dependency installation handles frozen libraries. The scope needs to be decided among excluding frozen dependencies, opting in with `--py`, overriding the target folder, and documenting the behavior; done should include agreed behavior and help text.

Written by the indexing model from the issue text.