Remove dependency on chrono module for further compatibility

[MarksBench]

Hello,

For your consideration - I'm using a Pi Pico and couldn't find the "chrono" module. I replaced the chrono timer usage with utime.ticks in perform_single_ref_calibration() and it seems to work. From:

def perform_single_ref_calibration(self, vhv_init_byte):
        chrono = Timer.Chrono()
        self._register(SYSRANGE_START, 0x01|vhv_init_byte)
        chrono.start()
                                    
        while self._register((RESULT_INTERRUPT_STATUS & 0x07) == 0):
            time_elapsed = chrono.read_ms()

To:

def perform_single_ref_calibration(self, vhv_init_byte):
        self._register(SYSRANGE_START, 0x01|vhv_init_byte)
        startTime = utime.ticks_ms()

        while self._register((RESULT_INTERRUPT_STATUS & 0x07) == 0):
            time_elapsed = utime.ticks_diff(utime.ticks_ms(), startTime)

I apologize for my poor GitHub usage - this (and the other issue) are my first two steps on this platform...

[2020gaurav]

Thanks, @MarksBench looks like Chrono is not available for in microphone 1.15.0 which i am using for my ESP32. you should raise a pull request with above fix.