Depend on compute core protocol

[intel352]

Summary

• replace the local compute protocol copy with aliases to workflow-plugin-compute-core/protocol
• declare workflow-plugin-compute-core as a plugin dependency
• keep the existing crypto catalog API stable for downstream consumers

Verification

• GOWORK=off go build ./...
• GOWORK=off go test ./... -v -race -count=1
• GOWORK=off go vet ./...
• GOWORK=off go run ./cmd/wfctl plugin validate-contract /Users/jon/workspace/workflow-plugin-crypto (from /Users/jon/workspace/workflow)
• git diff --check