fix(server): enforce browse continuation point limit at capacity

[MrAlaskan]

Fixes an off-by-one error in browse continuation-point retention by evicting the oldest point as soon as the session reaches MaxBrowseContinuationPoints, and adds a regression test covering the exact-limit case that previously allowed one extra browse continuation point to remain active.

[marcschier]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.53%. Comparing base (84fa8e8) to head (8338849).
⚠️ Report is 12 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4036      +/-   ##
==========================================
- Coverage   73.85%   73.53%   -0.33%     
==========================================
  Files        1345     1345              
  Lines      179988   180040      +52     
  Branches    31668    31679      +11     
==========================================
- Hits       132938   132397     -541     
- Misses      36299    36940     +641     
+ Partials    10751    10703      -48     

Files with missing lines	Coverage Δ
...Opc.Ua.Server/Session/SessionContinuationPoints.cs	98.42% <100.00%> (ø)

... and 48 files with indirect coverage changes

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