CLPR-6.4: Ethereum Payment Layer Functions

## Story CLPR-6.4: Ethereum Payment Layer Functions

**Parent Epic:** CLPR-6: Ethereum On-Chain Service
**Repo:** TBD

### Objective

Implement connectors, slashing, and endpoint bonds on Ethereum.

### Acceptance Criteria

- **AC-1:** `registerConnector` — Permissionless, payable (`msg.value = initialBalance + stake`).
- **AC-2:** `topUpConnector` — Connector admin, payable.
- **AC-3:** `withdrawConnectorBalance` — Connector admin. Not stake. Minimum enforced.
- **AC-4:** `deregisterConnector` — Connector admin. Returns balance + stake. Fails with pending messages.
- **AC-5:** `getConnector` — Query.
- **AC-6:** Slashing: geometric escalation, ban after threshold, proceeds to submitting endpoint.
- **AC-7:** Source-side slashing on failure response arrival.
- **AC-8:** `registerEndpoint(bytes32, bytes)` — Permissionless, payable (bond). Bond lockup period (`BOND_LOCKUP_BLOCKS`).
- **AC-9:** `deregisterEndpoint(bytes32)` — Endpoint account only. Returns bond after lockup.
- **AC-10:** Per-Connector queue quota and fee escalation.
- **AC-11:** Reentrancy guard + CEI on all fund transfers.
- **AC-12:** Events: `ConnectorRegistered`, `ConnectorDeregistered`, `EndpointRegistered`, `EndpointDeregistered`, `ConnectorSlashed`.
- **AC-13:** Foundry tests: register/top-up/withdraw/deregister, slashing, ban, endpoint bond lifecycle, queue quota, fee escalation.

### Dependencies

- CLPR-6.3

### Risk

**Medium** — Fund handling, reentrancy protection, bond lockup timing.

Start with dependency CLPR-6.3 and the Ethereum On-Chain Service context, then map the listed connector and endpoint functions to their contract entry points. Done means all acceptance criteria are implemented, including fund-safety controls, slashing and lockups, emitted events, and the specified Foundry test coverage.

Written by the indexing model from the issue text.