fix: extract nested schemaTypes from arrays in Fastify routes

[eropple]

Summary

Fixes a bug where nested schemaType-wrapped schemas inside Type.Array were not being extracted to components/schemas when used in Fastify routes.

Example that was broken:

const Inner = schemaType("Inner", Type.Object({ foo: Type.String() }));
const Outer = schemaType("Outer", Type.Object({ 
  items: Type.Array(Inner)  // Inner was not extracted!
}));

Root Cause

findTaggedSchemasInSchemas used TypeBox's Type.IsArray() to detect array schemas. However, Type.IsArray() relies on an internal ~kind property that Fastify strips during schema processing. This caused the array detection to fail, so nested schemas within arrays were never discovered.

Fix

Replace Type.IsArray(s) with a direct JSON Schema check: s.type === 'array' && s.items !== undefined. This approach works regardless of whether TypeBox's internal metadata is present.

Test Plan

• Added test for basic nested schemaType in arrays
• Added test for deeply nested arrays (array of arrays)
• Added test for nullable arrays via Type.Union
• Added test that schema symbols survive route handler processing
• All 80 tests pass