update msc sdcad example to work with metro rp2040

[hathach]

This pull request introduces improvements to SD card handling and code style consistency in two example files: msc_external_flash_sdcard.ino and msc_sdfat.ino. The changes include adding SD card configuration for the ARDUINO_ADAFRUIT_METRO_RP2040 board, enhancing SD card initialization logic, and cleaning up code formatting for better readability.

SD Card Configuration Updates:

• Added specific SDCARD_CS, SDCARD_DETECT, and SDCARD_DETECT_ACTIVE definitions for the ARDUINO_ADAFRUIT_METRO_RP2040 board in msc_external_flash_sdcard.ino and msc_sdfat.ino, ensuring compatibility with this board. [1] [2]

SD Card Initialization and Logic Improvements:

• Updated init_sdcard() and sdcard_ready_callback() to use the new SDCARD_DETECT_ACTIVE macro, improving flexibility for boards with different active states for SD card detection. [1] [2]
• Replaced the hardcoded chipSelect variable with SDCARD_CS in msc_sdfat.ino for consistency with the updated configuration.

Code Formatting and Readability Enhancements:

• Reformatted function definitions (init_sdcard, print_rootdir, and loop) to use a consistent inline style for braces, aligning with modern C++ coding standards. [1] [2] [3]
• Removed unnecessary blank lines in msc_external_flash_sdcard.ino to improve code readability.