Add UUID to manifest and verify integrity before decompression

- Add UUID field to both inner and outer manifest messages
- Generate random v4 UUID when creating manifest
- Hash compressed data (not uncompressed) for integrity check
- Verify hash before decompression to prevent malicious payloads
- Validate UUIDs are proper format and match between inner/outer
- Sign string format: MAGIC-UUID-MULTIHASH

mfer/mf.proto

@@ -28,6 +28,9 @@ message MFFileOuter {
     int64 size = 103;
     bytes sha256 = 104;
 
+    // uuid must match the uuid in the inner message
+    bytes uuid = 105;
+
     bytes innerMessage = 199;
     // 2xx for optional manifest root attributes
     // think we might use gosignify instead of gpg:
@@ -72,6 +75,10 @@ message MFFile {
     // required manifest attributes:
     repeated MFFilePath files = 101;
 
+    // uuid is a random v4 UUID generated when creating the manifest
+    // used as part of the signature to prevent replay attacks
+    bytes uuid = 102;
+
     // optional manifest attributes 2xx:
     optional Timestamp createdAt = 201;
 }