Support OpenAPI v3.2 feature - Multipurpose Tags with Nesting

TLDR; Can support for the new [Tags object](https://spec.openapis.org/oas/v3.2.0.html#tag-object) in OpenAPI v3.2 be added to Huma?

OpenAPI v3.2 introduces the feature of Multipurpose Tags with Nesting.

This allows for nested tag grouping which enables a cleaner structure. Huma currently just supports a list of strings as tags, but it would be great if support for the new [Tags object](https://spec.openapis.org/oas/v3.2.0.html#tag-object) could be added. That allows the renderers such as Stoplight Elements and Scalar docs to use this nesting to render cleaner docs.

OpenAPI release note: https://www.openapis.org/blog/2025/09/23/announcing-openapi-v3-2

Start by reading the OpenAPI v3.2 Tag Object specification and inspecting Huma's current handling of tags in its OpenAPI output. Compare the existing string-list behavior with the nested, multipurpose Tags object and consider how generated documents are consumed by Stoplight Elements and Scalar. Done means Huma can represent and emit the requested nested tag structure for those renderers.

Written by the indexing model from the issue text.