Scriptconfig

Added

* The "type" of a `Value` can now be set to "smartcast:legacy" for explicit old behavior or "smartcast:v1" for the new candidate behavior.

Changed

* The `Value` class can now take `default` as a keyword argument for better
interoperability with argparse. We may remove the `value` keyword in the
future in favor of this.

* The `smartcast` `allow_split` now works, and defaults to "auto", which will prepare us for a backwards incompatible change to remove the auto string split behavior.

Fixed

* Fix issue with internal argparse change in CPython125355


Added
* Add experimental new method `DataConfig.cls_from_argparse` which dynamically
creates a scriptconfig object from an existing argparse object. Some advanced
argparse options may not be supported.

Added

* New convenience arguments to `.cli`
* Support for 3.13

Add
* Add experimental new flag `__allow_newattr__` which relaxes the constraint
that you can't add keys on the fly.

Removed

* Remove 3.6 and 3.7 support


Fix:
* Fixed the `define` method.
* Initial implementation of `port_from_click`

Added
* Allow special options to be passed to cli

Changed
* Better error messages when parsing argv
* Add a docstring to `DataConfig`

Fixed
* Fix issue caused by a CPython patch https://github.com/python/cpython/pull/115674