fix(gcp/computeengine): a short non-empty idempotency token silently drops the insert RequestId #488

Problem

providers/gcp/services/computeengine/client.go (:873) sets the commitment insert RequestId from common.IdempotencyGUID(token), which returns "" for a non-empty token shorter than 32 hex chars. The RequestId is then silently dropped. idempotentCommitmentName (:1436-1442) already rejects non-hex tokens earlier, and the deterministic commitment name still dedupes a re-drive, so the remaining gap is a short all-hex token (e.g. abc) losing request-level idempotency without any error.

Expected

Use common.OrderIDFromToken (added in #487) or an equivalent check so a non-empty token that cannot form a GUID fails before the insert, and replace the package's unexported errInvalidIdempotencyToken (~:1451) with common.ErrInvalidIdempotencyToken. Needs the GCP pkg pin bumped past #487 (GCP pins a different pkg version than Azure).

Found while planning #104 (A09-020). Real producers (DeriveIdempotencyToken, 64-char hex) are unaffected.