This PR was created by Knope. Merging it will create a new release

### Breaking Changes

#### `const` values in responses are now validated at runtime

Prior to this version, `const` values returned from servers were assumed
to always be correct. Now, if a server returns
an unexpected value, the client will raise a `ValueError`. This should
enable better usage with `oneOf`.

PR #1024. Thanks @peter-greenatlas!

#### Switch YAML parsing to 1.2

This change switches the YAML parsing library to `ruamel.yaml` which
follows the YAML 1.2 specification.
[There are breaking
changes](https://yaml.readthedocs.io/en/latest/pyyaml/#defaulting-to-yaml-12-support)
from YAML 1.1 to 1.2,
though they will not affect most use cases.

PR #1042 fixes #1041. Thanks @rtaycher!

### Features

- allow Ruff 0.4 (#1031)

### Fixes

#### Fix nullable and required properties in multipart bodies

Fixes #926.

> [!WARNING]
> This change is likely to break custom templates. Multipart body
handling has been completely split from JSON bodies.

Co-authored-by: GitHub <[email protected]>