`GET /eth/v1/builder/header/...` `duration > 950 ms`

MEV boost has this option:
```
-request-timeout-getheader int
timeout for getHeader requests to the relay [ms] (default 950)
```

This value (950 ms) is chosen to be slightly less than the `BUILDER_PROPOSAL_DELAY_TOLERANCE=1 sec` [spec value](https://github.com/ethereum/builder-specs/blob/main/specs/bellatrix/validator.md#constants) to allow some network latency between the beacon node and MEV boost.

However, I often see the `duration` field in the `GET /eth/v1/builder/header/...` log higher than that:

Examples with `v1.11`
```
INFO[XXXT00:25:12.121Z] http: GET /eth/v1/builder/header/... 200 duration=0.982362 method=GET path=/eth/v1/builder/header/... status=200 version=v1.11.0
```

And even with `v1.12`, > 1 second:
```
level=info msg="http: GET /eth/v1/builder/header/... 200" duration=1.010395 method=GET path=/eth/v1/builder/header/... status=200 version=1.12
```

The consequence of that is, even if MEV boost already has some relays bid, the connected beacon node falls back on the locally built block after the `BUILDER_PROPOSAL_DELAY_TOLERANCE` cutoff.