[colegarien]

sdcard imported fmt only for fmt.Errorf, one fmt.Sprintf in NewCID, and fmt.Printf in CSD.Dump. This pulls fmt, strconv and reflect into any program using the driver, even if it never prints.

• Replace fmt.Errorf with package level sentinel errors in errors.go. This also stops allocating on every error.
• Build CID.ProductVersion from bytes. The field is still a string.
• Keep CSD.Dump with the same hex output, using print and a small helper.
• ReadData now returns the real waitStartBlock error.

Behavior changes

• All error messages changed and now start with "sdcard: ".
• The two CMD8 errors are now separate errors and no longer include the status byte.
• The init_card_v1 error no longer ends with "\r\n".
• Dump output goes through print instead of fmt.Printf.

Size

STM32F103 program mounting the card as LittleFS through tinyfs, TinyGo 0.44.0, 512 KB flash linker script.

	v0.37.0	fmt free
flash	91.4 KB	47.0 KB
RAM	5.6 KB	4.4 KB

Testing

• gofmt -l sdcard is clean
• tinygo build -target=feather-m4 ./examples/sdcard/console/ builds
• Hardware test on a Blue Pill with the v0.37.0 based copy