feat(replication): SSE-C ciphertext passthrough replication (#5898)

Complete the encrypted-object replication series (backlog#1783, PR-C of
3, after #5872 and #5885): SSE-C objects replicate as ciphertext
passthrough — the source holds no customer key, so the stored bytes and
their encryption metadata travel verbatim and the replica decrypts only
with the original customer key, single-part and multipart.

- Sender: SSE-C objects read raw (raw_data_movement_read), transfer at
  ciphertext size, and range multipart parts over stored part sizes.
- Receiver: authorized replication PUTs restore the stored SSE-C keys
  from the transport headers (exact lowercase forms - the read-path
  check is case-sensitive), set ObjectOptions.preserve_ciphertext, and
  skip compression, bucket-default SSE, and sse_encryption behind one
  restore-derived gate. Multipart uses an internal session marker to
  store parts verbatim and strips it on complete.
- Convergence: the replication HEAD sends
  x-rustfs-source-replication-check; the target authorizes it as
  ReplicateObjectAction and skips SSE-C read validation for that
  request only, so keyless convergence HEADs see etag/size/mtime
  instead of 400 and SSE-C replicas stop re-driving forever.
- e2e: SSE-C contract flips to a key-gated readable replica (no-key and
  wrong-key GETs fail - the direct silent-plaintext detector); new
  multipart passthrough contract with ETag/marker/stability assertions.

crates/ecstore/src/object_api/types.rs

@@ -253,6 +253,11 @@ pub struct ObjectOptions {
     /// fence avoids recursively acquiring the read lock behind a queued writer.
     pub bucket_lifecycle_lock_fence: Option<NamespaceLockFence>,
     pub replication_request: bool,
+    /// Authorized SSE-C replication passthrough: the body is already
+    /// ciphertext, so the write path must not encrypt or compress it and
+    /// stores the restored encryption metadata verbatim. Only the
+    /// replication-authorized options builders may set this.
+    pub preserve_ciphertext: bool,
     pub delete_marker: bool,
     pub synthetic_version_id: bool,