Fix auto_map_topic_alias_send logic

[smaeul]

Previously, it would always remove the topic name when adding the alias, even the first time, so the mapping would not be set on the server, and the server would reject the packet.

[redboltz]

I think your fix is correct. In the LRU case, the behavior should be “register the topic alias,” not “use the topic alias.”
However, it looks like the CI is reporting failures (I’ve re-run it several times).

I suspect that the expected value in the test might be wrong. Could you take a look?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.91%. Comparing base (fe389da) to head (2328d15).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #55      +/-   ##
==========================================
+ Coverage   90.89%   90.91%   +0.01%     
==========================================
  Files          55       55              
  Lines        7460     7470      +10     
==========================================
+ Hits         6781     6791      +10     
  Misses        679      679              

Files with missing lines	Coverage Δ
src/mqtt/connection/core.rs	86.36% <100.00%> (ø)
src/mqtt/packet/v5_0/publish.rs	94.52% <100.00%> (+0.03%)	⬆️

... and 6 files with indirect coverage changes

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[redboltz]

Thank you for updating.