CUSIP length constraints corrected on fixed income schemas

Broker API

The cusip field on the us_treasury and us_corporate schemas now has minLength and maxLength of 9, matching its documented nine-character CUSIP format and existing ^[A-Z0-9]{9}$ pattern.

• Previously the length bounds were 12, so no value could satisfy both the length and the pattern.
• The sibling isin fields keep their 12-character constraints.

Affected Endpoints

• GET /v1/assets/fixed_income/us_treasuries
• GET /v1/assets/fixed_income/us_corporates