test: avoid getFreePort collisions

[ndr-brt]

What this PR changes/adds

Add an ALREADY_RETURNED HashSet to ensure that the port generated by getFreePort is not already returned.

Why it does that

Avoid possible collisions.

Further notes

• changed the "incremental" port generation to the complete randomic. Looking at the tests they are always calling the getFreePort without arguments, that is generating a random number anyway, so the "efficiency" of using the next number instead is pretty negligible.

Linked Issue(s)

Closes #4365

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Codecov Report

Attention: Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 74.91%. Comparing base (7f20ba5) to head (433f7df).
Report is 362 commits behind head on main.

Files	Patch %	Lines
...b/src/main/java/org/eclipse/edc/util/io/Ports.java	90.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4366      +/-   ##
==========================================
+ Coverage   71.74%   74.91%   +3.17%     
==========================================
  Files         919     1066     +147     
  Lines       18457    21383    +2926     
  Branches     1037     1171     +134     
==========================================
+ Hits        13242    16020    +2778     
- Misses       4756     4839      +83     
- Partials      459      524      +65     

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