kms/service.rs re-declared x-rustfs-encryption-key-id and x-rustfs-encryption-algorithm locally; the canonical owners live in rustfs-utils' object_encryption_keys module, which kms already transitively builds. Enable the http feature on the existing rustfs-utils dependency and import the two constants instead. The explanatory comment about why the algorithm header exists (SSE mode vs AEAD cipher round-trip) moves to the import site.
No dependency-graph change (cargo tree -p rustfs-kms is unchanged apart from the feature) and no behavior change: the imported values are byte-identical.
Ref rustfs/backlog#1833 (PR2).