Fix IndexError in convert_size_bytes_to_string for sizes >= 1024 YB

[SAY-5]

Describe your changes
convert_size_bytes_to_string() raised IndexError for any size of 1024 YB or more (2**90 bytes and up), because the unit-selection loop guard factor <= factor_limit let the index increment one past the last SIZE_UNITS entry before units[factor] was read. Changing the guard to factor < factor_limit stops at the largest unit and clamps the value to YB instead of crashing. Smaller sizes are unaffected.

Related issue
#184

Checklist before requesting a review

• I have performed a self-review of my code.
• I have added tests for the proposed changes.
• I have run the tests and there are not errors.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.33%. Comparing base (c98dbf6) to head (b6bc4f3).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #186   +/-   ##
=======================================
  Coverage   98.33%   98.33%           
=======================================
  Files          13       13           
  Lines         780      780           
=======================================
  Hits          767      767           
  Misses         13       13           

Flag	Coverage Δ
unittests	98.33% <100.00%> (ø)

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[fabiocaccamo]

@SAY-5 thank you for this PR, could you please add tests for converting from string to size and also ensure that size -> string -> size returns the initial value?