feat: add OpenAPI error response support (issue #23)

[18IsabellaM]

• This PR depends on functionality added to a forked version of the openapiv3 crate, which I also have up for review in a separate PR. kurtbuilds/openapiv3#7
• This PR helps resolve issue #23.

PR Description:

This PR improves the OpenAPI spec generation by correctly capturing and displaying error status codes and their descriptions.

Changes made:

• Updated the OpenAPI generator to automatically include error responses derived from handlers that return errors as (StatusCode, String) tuples.

• Added support for grouping multiple error messages under the same status code:

  • If a handler returns the same status code with different messages, those messages will now be collected into a list in the OpenAPI spec.
  • Example:

  Err((StatusCode::BAD_REQUEST, "Invalid email".into()))
  Err((StatusCode::BAD_REQUEST, "Missing field 'username'".into()))

  Will produce the following OpenAPI response entry:

  "400":
    description: |
      - Invalid email
      - Missing field 'username'

• Added a new test case: 04-status_code.rs and a corresponding snapshot: 04-status_code.yaml.

• Improved the test framework to compare parsed YAML structures instead of raw strings, preventing failures due to key ordering differences.

[18IsabellaM]

• Note: Using a Git branch here due to unmerged functionality in the openapiv3 repo that introduces a helper method: kurtbuilds/openapiv3#7
• Once merged upstream, this can be changed back to the released version.

[kurtbuilds]

you can also use an (uncommitted) .cargo/config.toml file with the following to keep the PR mergeable:

[patch.crates-io]
openapiv3-extended = { path = "path/to/modified/local/copy" }

[18IsabellaM]

@kurtbuilds fixed it

[18IsabellaM]

• Note: Using a Git branch here due to unmerged functionality in the openapiv3 repo that introduces a helper method: kurtbuilds/openapiv3#7
• Once merged upstream, this can be changed back to the released version.

[18IsabellaM]

Hey @kurtbuilds , I’ve opened a PR adding new functionality for error responses. When you have a chance, could you please review and consider merging it? Thanks so much!

[kurtbuilds]

Thanks. I was fixing these merge conflicts but didn't finish last night. I'll get this over the line and published this weekend. Thank you for the contribution! IIRC, there's 1 failing test to be fixed. Welcome your help on that.

[18IsabellaM]

Just ran just test and cargo test --all -all-features everything passed on my end, but let me know if I’m missing something. Happy to dig in more!

[jkleinknox]

Should be BTreeMap to enforce deterministic order

[jkleinknox]

Hi @kurtbuilds I pushed an update to change HashMap to BTreeMap to ensure deterministic order. So the PR is ready to be reviewed again. Thanks.