feat: add PutContractRequest/PutContractResponse for delegate contract PUT

[sanity]

Summary

Adds message types to allow delegates to store new contracts via PUT operation.

Part of freenet/freenet-core#2829 (Delegate capability: Contract PUT).

Changes

New types in delegate_interface.rs

• PutContractRequest: Request to store a new contract

  • contract: ContractContainer - the contract code and parameters
  • state: WrappedState - the initial state
  • related_contracts: RelatedContracts<'static> - dependencies
  • context: DelegateContext - for context propagation
  • processed: bool - processing flag

• PutContractResponse: Response after PUT attempt

  • contract_id: ContractInstanceId - the contract that was stored
  • result: Result<(), String> - success or error message
  • context: DelegateContext - for context propagation

Enum updates

• OutboundDelegateMsg::PutContractRequest added
• InboundDelegateMsg::PutContractResponse added
• Helper methods updated (processed, get_context, get_mut_context, into_owned)
• From implementations added

Client serialization

• Added stub for PutContractRequest in client_events.rs (logs error if reached, as it should be handled by executor)

Testing

• All existing tests pass
• Types serialize/deserialize correctly

[AI-assisted - Claude]