test: add Go native fuzz tests for schema generation
Four fuzz targets exercising the schema pipeline:
- FuzzResolveSchemaType: arbitrary TypeAnnotation trees through the
recursive resolver
- FuzzJSONSchema: random SchemaType trees through JSON Schema rendering
- FuzzParsePredictor: arbitrary bytes as Python source through the
tree-sitter parser
- FuzzParseTypeAnnotation: arbitrary return type strings in predict
signatures
Includes:
- mise task 'test:fuzz' (FUZZTIME=30s per target by default)
- CI job 'fuzz-go' running 30s per target on Go changes
- Byte encoder/decoder for deterministic TypeAnnotation and SchemaType
tree construction from fuzz corpus
