fix(ssv): send SSV node operator ID as numeric uint64

[dnstaked]

Problem

The SSV node /v1/validators API expects the operators field as []uint64, but request_ssv_pubkeys_from_ssv_node serialized the operator ID directly from an alloy U256. serde emits U256 as a hex string (e.g. "0x64"), so the request body was {"operators":["0x64"]}.

The SSV node rejects this with:

400 Bad Request: json: cannot unmarshal string into Go struct field ValidatorsRequest.operators of type uint64

PBS then logs a warning and silently falls back to the public api.ssv.network API, so registry muxes never actually use the configured local SSV node.

Fix

Narrow the operator ID to a u64 before building the JSON body so it serializes as a number ({"operators":[100]}). A bounds check guards against an out-of-range ID instead of panicking.

Testing

• Added a regression test (ssv_node_request_serializes_operator_as_number) asserting the old U256 path emits "0x64" and the fixed path emits 100.
• cargo test -p cb-common interop::ssv::utils passes.
• Verified live against a Hoodi SSV node: {"operators":[100]} returns 200 with the validator list, where {"operators":["0x64"]} returns 400.

Made with Cursor