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.

color.go

@@ -0,0 +1,13 @@
+package bambunfc
+
+import "fmt"
+
+// Color is an RGBA filament color from a Bambu tag.
+type Color struct {
+	R, G, B, A uint8
+}
+
+// Hex returns "#RRGGBBAA" with uppercase hex digits.
+func (c Color) Hex() string {
+	return fmt.Sprintf("#%02X%02X%02X%02X", c.R, c.G, c.B, c.A)
+}