errors.rs — duplicate error discriminants 42 and 43

[JSE19]

Description:
contracts/escrow/src/errors.rs lines 95, 97, 101, 103: BasketTokenMismatch = 42 and TooManyMessages = 42 share the same discriminant 42. InvalidMulticallArg = 43 appears twice (lines 97 and 103). Since these discriminants are part of the public contract ABI, clients cannot distinguish BasketTokenMismatch from TooManyMessages, or the two InvalidMulticallArg variants.
Acceptance Criteria:

• All ContractError discriminants are unique
• No duplicate numeric values in the enum
• Existing error codes (1-41) remain unchanged to preserve ABI compatibility