fix(deps)!: update module github.com/getkin/kin-openapi to v0.132.0

This is flagged as a breaking change as it could break consumers, as
`kin-openapi` requires a minimum source compatibility (via `go`) of
1.22.

This is still a deprecated version of Go (which ran out of support on
2025-02-11), so is still outdated, and therefore shouldn't be /that/
breaking.

However, we should make it clear.

This also fixes an issue noted in [0] and [1], where the request body
was not available to handlers after being processed by the
`openapi3filter`.

[0]: https://togithub.com/oapi-codegen/nethttp-middleware/pull/22
[1]: https://togithub.com/getkin/kin-openapi/issues/743

fix: correct error code

This error path shouldn't be happening very often, but we should still
correct the error code used.

refactor: migrate `error` to a method parameter, not part of `ErrorHa…

…ndlerOpts`

While writing the documentation for this, it didn't feel quite right to
note that the `error` wasn't part of the method signature, despite it
being very important for the actual handling of errors.

fix(deps): update module github.com/getkin/kin-openapi to v0.124.0

Correct package name

I thought I'd already done this 😅

Add `net/http` validation

To show how one may use this middleware with a plain `net/http` server.