Verify Metadata Struct Fields after Compilation

[maennchen]

Fixes

https://discord.com/channels/711271361523351632/1037049265836535868/1420674638622752788

== Compilation error in file lib/ash_authentication/strategies/magic_link.ex ==
** (UndefinedFunctionError) function AshAuthentication.Strategy.MagicLink.__struct__/0 is undefined (function not available)
    AshAuthentication.Strategy.MagicLink.__struct__()
    /Users/.../code/kloevaa/deps/spark/lib/spark/dsl/extension.ex:1515: (module)
    (spark 2.3.3) lib/spark/dsl/extension.ex:1253: Spark.Dsl.Extension.build_entity/8
could not compile dependency :ash_authentication, "mix compile" failed. Errors may have been logged above. You can recompile this dependency with "mix deps.compile ash_authentication --force", update it with "mix deps.update ash_authentication" or clean it with "mix deps.clean ash_authentication"

The issue is that the struct module may not be fully compiled when checking and in that case, the __struct__/0 function does not yet exist. Moving the check into after_verify.

Tests

This does not contain a test. I don't know how I would test this without starting a Parallel Compiler and having a circular dependency. And that would probably mean running a full small fixture mix project.

Contributor checklist

Leave anything that you believe does not apply unchecked.

• I accept the AI Policy, or AI was not used in the creation of this PR.
• Bug fixes include regression tests
• Chores
• Documentation changes
• Features include unit/acceptance tests
• Refactoring
• Update dependencies

[zachdaniel]

One thing to note (and I think this was already the case from my impl) is that this doesn't check nested entities (entities inside entities).