The picoschema enum-with-description syntax `[val1, val2], description`
is invalid YAML. Users must quote it so YAML parses it as a string.
This adds `_parse_enum_string()` to extract enum values and description
from the resulting string value (e.g., "[active, blocked], current state").
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: phernandez <paul@basicmachines.co>