[PMPOSU-777]: [avrogen] feat: Handle references to previous defined schema in top-level record types

[eft-prima]

https://prima-assicurazioni-spa.myjetbrains.com/youtrack/issue/PMPOSU-777

This pull request fixes a bug in the Avrogen.Schema.external_dependencies function, ensuring that previously defined types within a schema are no longer incorrectly identified as external dependencies. The changes include refactoring the implementation to properly track defined types, updating tests to cover these cases, and bumping the package version.

Bug fix and implementation improvements

• Refactored the external_dependencies function in lib/avrogen/schema.ex to track previously defined types and exclude them from external dependencies. This includes introducing the handle_field helper and correctly handling unions and named types.

Testing enhancements

• Added new test cases in test/schema_test.exs to verify that previously defined types (with and without namespace) are not identified as external dependencies.

Documentation and release

• Updated the CHANGELOG.md to document the bug fix for external dependencies detection.
• Bumped the version in mix.exs from 0.9.0 to 0.10.0 to reflect the new release.

[EddieWhi]

Slack conversation for prosperity:
Eddie Whiteside
Nice, thanks Ed 🙂
What I can't work out from the PR is how it worked previously with the more nested types???

Ed Fawcett-Taylor
Ah, so that's because Avrogen.Schema.external_dependencies never looked at more nested types, it just looked at the types of the fields in a top level "record" type. The resolving of more nested types is done by Avrogen.Avro.Schema.generate_code , which doesn't have the same issue.
This PR fixes my immediate problem but it wouldn't handle a situation where there's a deeply nested reference to an actual external type.

Eddie Whiteside
Oh... it didn't recurse atall? So you can't have an external type at a more nested level.
Right!
I see.

Ed Fawcett-Taylor
Yeah, still work to be done but this was the smallest change I could do that would unblock me!

Eddie Whiteside
For sure.

[cpiemontese]

+1 from me, if you run suite-py bump you can also update the CHANGELOG file (or you can update it manually) so we keep everything aligned and then I'll release

[eft-prima]

+1 from me, if you run suite-py bump you can also update the CHANGELOG file (or you can update it manually) so we keep everything aligned and then I'll release

Oh cool, I didn't know it did that! Done.