Introduce a new simulated backend implementation under ethclient/simulated and migrate bind-facing wrappers/tests to use it.
Key changes:
- Add the new backend entry points and behavior in ethclient/simulated, including chain control helpers used by tests (commit/rollback/fork/time adjustment).
- Update legacy bind wrappers in accounts/abi/bind/backends to delegate to the new simulated backend while preserving old APIs.
- Align bind v2/backend and utility tests to the new simulated backend client surface and transaction flow.
- Refresh abigen/bind tests and shared interfaces impacted by the backend migration.
Compatibility notes:
- Keep backward-compatible wrapper constructors for existing contract test code.
- Preserve legacy transaction paths in tests while supporting EIP-1559-aware flows where applicable.
Validation:
- Verified affected packages compile and pass tests.
- Verified repository-wide go test ./... passes after follow-up compatibility fixes.
