fix(moderate): add bounds checking to prevent buffer overflow in example

[lahirunirmalx]

• Add bounds check for single-ended channel selection (0-7)
• Add bounds check for differential channel selection (0-3)
• Add bounds check for PGA selection (0-6)
• Add bounds check for DRATE selection (0-15)
• Add bounds check for register read (0-10)
• Add bounds check for register write (0-10)
• Print error messages for invalid inputs instead of crashing
• Add confirmation message for register write operations

Prevents undefined behavior when user sends out-of-range values via serial