Add UX Sync unit tests

[nroggeman-ledger]

Description

The goal of this PR is to add unit-tests for UX Sync library, in order to improve code coverage of this library

Changes include

• Bugfix (non-breaking change that solves an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)
• [*] Tests
• Documentation
• Other (for changes that might not fit in any category)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 57.14286% with 3 lines in your changes missing coverage. Please review.

Project coverage is 60.32%. Comparing base (9a9e153) to head (a940eb3).

Files with missing lines	Patch %	Lines
lib_ux_sync/src/ux_sync.c	57.14%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #746      +/-   ##
==========================================
+ Coverage   59.89%   60.32%   +0.42%     
==========================================
  Files          12       13       +1     
  Lines        1723     1807      +84     
==========================================
+ Hits         1032     1090      +58     
- Misses        691      717      +26     

Flag	Coverage Δ
unittests	60.32% <57.14%> (+0.42%)	⬆️

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