Fix: Allow HardwareI2C::requestFrom to return values > 256

[aentinger]

Changing return type of requestFrom from uint8_t to size_t allows the function to return the correct amount of bytes read (since internally it's already a size_t which is downcast to a uint8_t upon returning it).

Merging this PR also requires to merge

• Fix requestFrom() return type for 16-bit lengths ArduinoCore-samd#442
• Fix: Allow HardwareI2C::requestFrom to return values > 256 ArduinoCore-megaavr#92
• Fix: Allow HardwareI2C::requestFrom to return values > 256 ArduinoCore-mbed#97

@facchinm Let's coordinate to get this done.

[codecov-io]

Codecov Report

Merging #132 (a553558) into master (4bd75df) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #132   +/-   ##
=======================================
  Coverage   96.40%   96.40%           
=======================================
  Files          14       14           
  Lines         835      835           
=======================================
  Hits          805      805           
  Misses         30       30           

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