fix(go): implement recursive schema reference resolution

[MichaelDoyle]

This change fixes "Reference must be canonical" validation errors when running actions through the JSON path (e.g., via the Dev UI).

The Go framework now:

1. Recursively resolves 'genkit:' schema references within nested objects and arrays in ResolveSchema.
2. Ensures schema resolution is performed in runJSONWithTelemetry before input validation.

This ensures that strict JSON schema validators see fully-resolved definitions rather than internal Genkit reference strings.

[gemini-code-assist]

Code Review

This pull request updates schema resolution in go/core/core.go to recursively resolve nested maps and arrays, and integrates this resolved schema in runJSONWithTelemetry within go/core/action.go. Feedback highlights that the test suite is missing coverage for a missing schema (which was removed) and circular references (which could cause a stack overflow). A code suggestion is provided to restore and add these tests.

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[apascal07]

@cabljac this is somewhat related to your work supporting the new JSON schema field in the Gemini plugin (and conversely allowing recursion/references in schema generation) I think, can we validate both pieces of work and make sure they work well together?

[MichaelDoyle]

@cabljac this is somewhat related to your work supporting the new JSON schema field in the Gemini plugin (and conversely allowing recursion/references in schema generation) I think, can we validate both pieces of work and make sure they work well together?

lemme know @cabljac @apascal07 -- I am also happy to back off from the slop cannon on this one. Right now, prompts with input schemas don't work on the dev-ui from what I can tell, so that's what I am aiming to fix.