tpu-client-next: test_config picks random port fix

[puhtaytow]

Problem

The test_config picks a random port (0), which might conflict with ports allocated deterministic way thru unique_port_range_for_tests.

Summary of Changes

• The function now picks non-overlapping port thru unique_port_range_for_tests
• Ipv4Addr::new(127, 0, 0, 1) was replaced by IpAddr::V4(Ipv4Addr::LOCALHOST) for consistency reason.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.0%. Comparing base (77f600b) to head (f7ce914).
⚠️ Report is 2334 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##           master    #7800     +/-   ##
=========================================
- Coverage    83.0%    83.0%   -0.1%     
=========================================
  Files         812      812             
  Lines      357199   357199             
=========================================
- Hits       296801   296754     -47     
- Misses      60398    60445     +47     

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[alexpyattaev]

YES PLEASE