test: fail on unexpected reconnect disconnect

[vibhor-aggr]

Summary

• make the reconnect regression fail if the client emits an extra unexpected disconnect
• keep the existing expected first disconnect assertion intact

Refs: #251

Verification

• ./node_modules/.bin/borp --timeout 180000 --expose-gc -p test/client-reconnect.js
• npm run lint -- test/client-reconnect.js
• git diff --check

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.24%. Comparing base (ac5394b) to head (cb34bac).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5412      +/-   ##
==========================================
- Coverage   93.25%   93.24%   -0.01%     
==========================================
  Files         110      110              
  Lines       36825    36825              
==========================================
- Hits        34340    34339       -1     
- Misses       2485     2486       +1     

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