Formulaic

This is a minor release with several important bugfixes.

**Bugfixes and cleanups:**

* Fixed intercept terms sorting after other features (by not counting literal
factors toward the degree of a term). 156
* Fixed a regression in 0.6.4 around quoted field names in Python evaluations. 154
* Fixed detection and dropping of null rows in sparse datasets. 155
* Fixed `poly()` transforms operating on datasets that include null values. 155
* Arguments can now be passed when running the unit tests using `hatch run tests`.

This is a minor release with several new features and cleanups.

**New features and enhancements:**

* Added support for keeping track of the source of variables being used to
evaluate a formula. Refer to the `ModelSpec` documentation for more details.

**Bugfixes and cleanups:**

* All functions and methods now have type signatures that are statically checked
during unit testing.
* Removed `OrderedDict` usage, since Python guarantees the orderedness of
dictionaries in Python 3.7+.
* Suppress terms/factors in model matrices for which the factors evaluate to
`None`.

This is a minor release with a bugfix.

**Bugfixes and cleanups:**

* Fixed a regression introduced in the previous release when materializing categorical encodings of variables with no levels.

This is a minor release with several bugfixes.

**Bugfixes and cleanups:**

* Fixed issues handling empty data sets in formulae that used categorical
encoding.
* Added the MIT license to distribution classifiers.

This is a minor release with one new feature.

**New features and enhancements:**

* Added support for treating individual categorical features as though they do not span the intercept (useful for intentionally generating over-specified model matrices in e.g. regularized models).

This is a major release with some important consistency and completeness
improvements. It should be treated as *almost* being the first release candidate
of 1.0.0, which will land after some small amount of further feature extensions
and documentation improvements.

**Breaking changes:**

Although there are some internal changes to API, as documented below, there are
no breaking changes to user-facing APIs.

**New features and enhancements:**

* Formula terms are now consistently ordered regardless of providence (formulae or
manual term specification), and sorted according to R conventions by default
rather than lexically. This can be changed using the `_ordering` keyword to
the `Formula` constructor.
* Greater compatibility with R and patsy formulae:
* for patsy: added `standardize`, `Q` and treatment contrasts shims.
* for patsy: added `cluster_by='numerical_factors` option to `ModelSpec` to enable
patsy style clustering of output columns by involved numerical factors.
* for R: added support for exponentiation with `^` and `%in%`.
* Diff and Helmert contrast codings gained support for additional variants.
* Greatly improved the performance of generating sparse dummy encodings when
there are many categories. 110 112 (thanks dbalabka)
* Context scoping operators (like paretheses) are now tokenized as their own special
type.
* Add support for merging `Structured` instances, and use this functionality during
AST evaluation where relevant.
* `ModelSpec.term_indices` is now a list rather than a tuple, to allow direct use when
indexing pandas and numpy model matrices.
* Add official support for Python 3.11.

**Bugfixes and cleanups:**

* Fix parsing formulae starting with a parenthesis.
* Fix iteration over root nodes of `Structured` instances for non-sequential iterable values.
* Bump testing versions and fix `poly` unit tests.
* Fix use of deprecated automatic casting of factors to numpy arrays during dense
column evaluation in `PandasMaterializer`. 122 (thanks effigies)
* `Factor.EvalMethod.UNKNOWN` was removed, defaulting instead to `LOOKUP`.
* Remove `sympy` version constraint now that a bug has been fixed upstream.

**Documentation:**

* Substantial updates to documentation, which is now mostly complete for end-user
use-cases. Developer and API docs are still pending.