Thermal Printer/ESCPOS Android Library For Printing

• added boolean gradient parameter to bitmapToHexadecimalString.
• Fix bluetooth Android 33 compatibility
• Set Default BluetoothDevice UUID in Bluetooth Connection
• Adding greyscale to printed images
• Update targetSdkVersion to 33
• Added connection timeout for TCP
• No printer connect timeout
• Bluetooth connection improvement
• Annotations nullable added
• Open cash box command added
• Optimization of text style command
• Adding attribute
• Adding attribute
• Chinese characters length issue fixed
• Empty line bug fixed
• Other improvements for image printing