I2C Glitches on SDA

Hi,
I am trying to port the [Etherkit Si5351 Library](https://github.com/etherkit/Si5351Arduino) to the Raspberry Pi Pico. The library builds fine on both the MBED and the Arduino-pico platforms. I haven't succeeded in getting everything to work on either platform, but the MBED platform shows occasional 0.25 uS glitches on SDA that go high from a low state, that the [Ardunio-Pico board library](https://github.com/earlephilhower/arduino-pico) doesn't have. I can provide Logic analyzer screenshots if it helps.
Thanks,
Rob

Start by reproducing the reported SDA glitches on the Raspberry Pi Pico under the MBED platform and compare them with the Arduino-pico platform using a logic analyzer. The issue mentions the Etherkit Si5351 Library and both board libraries; done means the intermittent 0.25 uS SDA transitions are explained and the MBED behavior is corrected or clearly documented.

Written by the indexing model from the issue text.