feat(beacon): add streaming raw API responses

[Savid]

Summary

• add streaming OpenRaw* methods for beacon states, blocks, and execution payload envelopes
• return response metadata with explicit body ownership, idempotent close, leak cleanup, and lifecycle metrics
• use a dedicated configurable raw HTTP client with HTTP/2 support, bounded concurrent response bodies, and explicit wire-encoding control
• share request and status handling with buffered raw fetches, including typed status errors and bounded error-body draining
• document streaming usage, timeout behavior, completeness checks, and concurrency constraints

Breaking changes

• expand the beacon.Node and api.ConsensusClient interfaces
• update api.NewConsensusClient to require separate regular and raw HTTP clients plus a raw-response observer

Validation

• go test ./... -count=10
• go test -race ./... -count=3
• Linux heap and RSS acceptance gates, including 50 concurrent real TLS HTTP/2 responses of 73,216,552 bytes each
• full 50-response buffered comparison on a high-memory host
• go vet with normal and acceptance build tags
• golangci-lint run ./...