Add DDO on-chain contract adapter

[anjor]

Summary

• add a local DDO scheduling/tracking interface and concrete on-chain adapter backed by ddo-client
• implement piece-granular payment setup, tx confirmation-depth polling, receipt event parsing, and allocation status reads
• add focused adapter tests and record the new ddo-client dependency

Testing

• go test ./service/dealpusher

Notes

• upstream ddo-client still requires a raw private key for write clients, so this adapter currently enforces signer/address matching at runtime until signer-based constructors exist

[parkan]

we will fix this upstream