Lodestar VC publishes validator registrations for withdrawn validators

### Describe the bug

```rocketpool_validator | Feb-07 06:26:18.431[] info: Validator statuses withdrawn=6, total=6
rocketpool_validator | Feb-07 06:26:18.910[] info: Published validator registrations to builder epoch=261622, count=6
```

one imagines that once a validator has been withdrawn it is no longer eligible for block proposals.

### Expected behavior

Lodestar VC should not call register_validator/prepare_beacon_proposer for exited and withdrawn validators.

### Steps to reproduce

_No response_

### Additional context

_No response_

### Operating system

Linux

### Lodestar version or commit hash

v1.15.0/5d93a62

No source file or test is named. Start by locating the Lodestar validator-client code that calls register_validator and prepare_beacon_proposer, then trace how exited and withdrawn statuses are represented using the reported v1.15.0 commit as context. Done means withdrawn validators are excluded from those calls and the behavior is covered by an appropriate existing test or reproduction.

Written by the indexing model from the issue text.