Migrate off go-tpm-tools' attest.proto usage

[alexmwu]

VerifiedCOSState depends on go-tpm-tools attest.proto for the AttestedCosState proto. This is fine for now, but we'd ideally like to have this library vend its own proto that are updated locally.

confidential-space/server/extract/cos_state.go

Line 8 in 7bc4c97

pb "github.com/google/go-tpm-tools/proto/attest"

Consider renaming the func and proto to have the same name like AttestedCOSState, VerifiedCOSState or ConfidentialSpaceState.

Additionally, VerifiedCOSState's signature is VerifiedCOSState(event_log cel.CEL, registerType uint8). It should instead take a cel.MRType from https://github.com/google/go-eventlog/blob/main/cel/canonical_eventlog.go#L21 as follows VerifiedCOSState(event_log cel.CEL, registerType cel.MRType)