feat: select runtime profile by placement

[intel352]

Summary

• add ProviderRuntimeContract.RuntimeProfileForRequirements for shared placement tuple matching
• route SupportsProduct through the shared runtime-profile lookup
• cover matching and unsupported executor behavior in protocol tests

Verification

• RED: with the production method absent, GOWORK=off go test ./protocol -run TestProviderRuntimeContractSelectsProfileForPlacementRequirements -count=1 failed because RuntimeProfileForRequirements was undefined
• GREEN: GOWORK=off go test ./protocol -run TestProviderRuntimeContractSelectsProfileForPlacementRequirements -count=1
• GOWORK=off go test ./... -count=1
• git diff --check