Modal

- Added validation that App `name`, if provided, is a string.

- The `app.function` decorator now raises an error when it is used to decorate a class (this was always invalid, but previously produced confusing behavior).

- The `modal app list` output has been improved in several ways:
- Persistent storage objects like Volumes or Dicts are no longer included (these objects receive an app ID internally, but this is an implementation detail and subject to future change). You can use the dedicated CLI for each object (e.g. `modal volume list`) instead.
- For Apps in a *stopped* state, the output is now limited to those stopped within the past 2 hours.
- The number of tasks running for each App is now shown.

- Added the `region` parameter to the `modal.App.function` and `modal.App.cls` decorators. This feature allows the selection of specific regions for function execution. Note that it is available only on some plan types. See our [blog post](https://modal.com/blog/region-selection-launch) for more details.

* Added deprecation warnings when using Python 3.8 locally or in a container. Python 3.8 is nearing EOL, and Modal will be dropping support for it soon.

* Deprecated the `Image.conda` constructor and the `Image.conda_install` / `Image.conda_update_from_environment` methods. Conda-based images had a number of tricky issues and were generally slower and heavier than images based on `micromamba`, which offers a similar featureset and can install packages from the same repositories.
* Added the `spec_file` parameter to allow `Image.micromamba_install` to install dependencies from a local file. Note that `micromamba` supports conda yaml syntax along with simple text files.