Add bambu-nfc dump parse, Key-A HKDF, and spool merge.

Parse filanfc-dump/v1 zip/JSON, Bambu 1K images, and merge stickers by tray UID. dump and mifare packages stay importable for a later common library.

kdf.go

@@ -0,0 +1,30 @@
+package bambunfc
+
+import (
+	"crypto/hkdf"
+	"crypto/sha256"
+	"fmt"
+)
+
+var kdfSalt = []byte{
+	0x9a, 0x75, 0x9c, 0xf2, 0xc4, 0xf7, 0xca, 0xff,
+	0x22, 0x2c, 0xb9, 0x76, 0x9b, 0x41, 0xbc, 0x96,
+}
+
+const kdfInfo = "RFID-A\x00"
+
+// KeysA derives the 16 MIFARE Key-A values for a Bambu tag from its chip UID.
+func KeysA(uid []byte) ([16][6]byte, error) {
+	var keys [16][6]byte
+	if len(uid) == 0 {
+		return keys, fmt.Errorf("%w: empty", ErrUID)
+	}
+	okm, err := hkdf.Key(sha256.New, uid, kdfSalt, kdfInfo, 16*6)
+	if err != nil {
+		return keys, fmt.Errorf("%w: hkdf: %v", ErrUID, err)
+	}
+	for i := range 16 {
+		copy(keys[i][:], okm[i*6:i*6+6])
+	}
+	return keys, nil
+}