breaking(go): Refactored primitives APIs to be consistent

[apascal07]

Lots of different changes here, mostly summarized by:

• All "developer path" code now panics instead of returning errors, this includes genkit.Init() and all Define*() functions. This allows to define primitives statically and allow for cleaner code. "User path" code returns errors to be handled and/or retried.
• Changed usage of jsonschema.Schema to map[string]any to be package agnostic.
• All Define*() now accept custom configs which are validated against the custom schema provided at definition.
• All primitives now have a veneer that accepts a reference of that type which may include an optional config.

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• Tested (manually, unit tested, etc.)
• Docs updated (updated docs or a docs bug required)