fix: scope Cancel request matching to the current session

[MrAlaskan]

Summary

This PR scopes Cancel request matching to the caller's session and adds regression tests that verify a request handle can no longer cancel work that belongs to another session.

Problem

According to OPC UA Part 4, Cancel applies to a request handle from the same session that issued the original request. The server should not use a client-supplied requestHandle to match outstanding requests across all sessions.

Previously, StandardServer.CancelAsync() validated the caller's session but then forwarded only the raw requestHandle to RequestManager.CancelRequests(). RequestManager iterated the global outstanding-request table and canceled every request whose ClientHandle matched, without checking the owning session. Since request handles are only session-scoped and different sessions can legitimately reuse the same value, one session could cancel another session's in-flight request.

Changes

• Pass the validated caller session id from StandardServer.CancelAsync() into RequestManager.CancelRequests().
• Restrict RequestManager.CancelRequests() to requests whose SessionId and ClientHandle both match the Cancel request.
• Update existing request-manager and publish-queue tests to pass the session id and add a regression test that proves matching request handles in different sessions no longer interfere with each other.

[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 73.55%. Comparing base (84fa8e8) to head (a879271).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4023      +/-   ##
==========================================
- Coverage   73.85%   73.55%   -0.31%     
==========================================
  Files        1345     1345              
  Lines      179988   179992       +4     
  Branches    31668    31668              
==========================================
- Hits       132938   132388     -550     
- Misses      36299    36905     +606     
+ Partials    10751    10699      -52     

Files with missing lines	Coverage Δ
src/Opc.Ua.Server/Server/RequestManager.cs	86.31% <100.00%> (+0.14%)	⬆️
src/Opc.Ua.Server/Server/StandardServer.cs	73.43% <100.00%> (+0.03%)	⬆️

... and 44 files with indirect coverage changes

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