test(eip7702): Data + Confirm/Authorization DTOs (+8 tests)

[TaprootFreak]

Summary

Stage 34 of the coverage push. Pure DTO tests for EIP-7702 wire shapes used in the RealUnit sell flow.

Cases

Target	Cases
`Eip7702Domain.fromJson`	1 — name + version + chainId + verifyingContract
`Eip7702TypeField.fromJson`	1 — name + type
`Eip7702Types.fromJson`	1 — `Delegation` + `Caveat` field lists
`Eip7702Message.fromJson`	1 — delegate / delegator / authority / caveats / salt
`Eip7702Data.fromJson`	1 — every top-level field + recursive nested DTO parse
`Eip7702AuthorizationDto.toJson`	2 — six-field round-trip; `chainId` / `nonce` accept both number and string (per source comment)
`Eip7702ConfirmDto.toJson`	1 — nested `delegation` + `authorization`

What's pinned

• The nested `fromJson` chain (`Eip7702Data` → `Eip7702Domain` / `Eip7702Types` / `Eip7702Message`) actually walks all the way down.
• `Eip7702AuthorizationDto.chainId` and `nonce` are typed `dynamic` on purpose so the wire-side number-or-string contract holds — covered explicitly.
• `Eip7702ConfirmDto.toJson` preserves both nested JSON shapes byte-for-byte.

Test plan

• `flutter test test/packages/service/dfx/models/payment/eip7702_dtos_test.dart` — all 8 pass
• `flutter analyze` clean on the new file
• CI green