…ighdicom into feature/seg_volumes

…volume

* Enforce repo-review rule PP302

PP302: Sets a minimum pytest to at least 6

Must have a `minversion=`, and must be at least 6 (first version to
support `pyproject.toml` configuration).

* Enforce repo-review rule PP305

PP305: Specifies xfail_strict

`xfail_strict` should be set. You can manually specify if a check should
be strict when setting each xfail.

* Enforce repo-review rule PP306

PP306: Specifies strict config

`--strict-config` should be in `addopts = [...]`. This forces an error
if a config setting is misspelled.

* Enforce repo-review rule PP307

PP307: Specifies strict markers

`--strict-markers` should be in `addopts = [...]`. This forces all
markers to be specified in config, avoiding misspellings.

* Enforce repo-review rule PP308

PP308: Specifies useful pytest summary

An explicit summary flag like `-ra` should be in `addopts = [...]` (print
summary of all fails/errors).

* Enforce pytest ≥ 7.3.2

This is the first version to support Python 3.12:
https://docs.pytest.org/en/stable/changelog.html#pytest-7-3-2-2023-06-10

* Enforce repo-review rule MY104

MY104: MyPy enables ignore-without-code

Must have `"ignore-without-code"` in `enable_error_code = [...]`. This
will force all skips in your project to include the error code, which
makes them more readable, and avoids skipping something unintended.

* Enforce repo-review rule MY105

MY105: MyPy enables redundant-expr

Must have `"redundant-expr"` in `enable_error_code = [...]`. This helps
catch useless lines of code, like checking the same condition twice.

* Enforce repo-review rule MY106

MY106: MyPy enables truthy-bool

Must have `"truthy-bool"` in `enable_error_code = []`. This catches
mistakes in using a value as truthy if it cannot be falsy.

Preparation for 0.23.0 release