Fix PI4IOE5V6408 initialization and checked input reads

[ainyan03]

What changes

• begin() never set the initialized flag, so isEnabled() always returned false for a PI4IOE5V6408. It now records whether the device ID register (0x01) could be read and is non-zero. The check runs on every call, so a changed port or address is probed again.
• getInputLevel() was not overridden, so it always reported a failure. It now reads the input status register (0x0F) with error checking, the same way as M5IOE1_Class. On an invalid pin, a null pointer or an I2C failure it returns false and leaves *level untouched.

Other methods are unchanged.

Checked

• Hardware, Tab5 (two PI4IOE5V6408 at 0x43 / 0x44), for each expander: isEnabled(), begin(), and getInputLevel() compared with digitalRead() on all 8 pins, plus an invalid pin and a null pointer.

	Before	After
isEnabled() after M5.begin()	false	true
getInputLevel(), pins 0-7	false (failure) on every pin	true, level equals digitalRead()
invalid pin / null	false, output untouched	false, output untouched

• Builds with Arduino 2.0.x (ESP-IDF 4.4) / 3.x and ESP-IDF 5.1 to 6.1 across ESP32, S3, C3, C5, C6, C61, H2 and P4.