Address code review feedback: fix resource disposal and code quality issues

[Copilot]

Applies actionable feedback from the automated code review on PR #1.

Resource Management

• Added using var to SaveDialog in CSV export to ensure disposal
• Fixed empty catch block in SubscriptionManager.Dispose() with diagnostic logging

Code Quality

• Extracted AllocatePort() static method to eliminate static field mutation from instance context
• Replaced implicit foreach filtering with explicit LINQ Where() in MonitoredItem_Notification
• Fixed KeyValuePair default check: matchingKvp.Value != null → !matchingKvp.Equals(default(...))
• Removed unused JavaScript variables (nodesets, counterVariable, etc.)

API Correctness

• Added ApplicationConfiguration parameter to CoreClientUtils.SelectEndpoint() call
• Reordered CertificateValidator initialization before Validate() to set up event handlers first

Infrastructure

• Updated NuGet.Config to use nuget.org source for CI/CD compatibility

Not Applied

Obsolete method warnings were not addressed - these methods are not deprecated in the current OPC Foundation SDK (v1.5+), and the build produces zero warnings.

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[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• crl.entrust.net
  • Triggering command: /usr/bin/dotnet dotnet restore (dns block)
  • Triggering command: /usr/bin/dotnet dotnet restore tests/OpcScope.Tests/OpcScope.Tests.csproj (dns block)
  • Triggering command: /usr/bin/dotnet dotnet restore --no-dependencies /home/REDACTED/work/OpcScope/OpcScope/tests/OpcScope.Tests/OpcScope.Tests.csproj --packages /home/REDACTED/work/OpcScope/.codeql-scratch/dbs/csharp/working/packages /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal /p:TargetFrameworkRootPath=/home/REDACTED/work/OpcScope/.codeql-scratch/dbs/csharp/working/emptyFakeDotnetRoot /p:NetCoreTargetingPackRoot=/home/REDACTED/work/OpcScope/.codeql-scratch/dbs/csharp/working/emptyFakeDotnetRoot (dns block)
• ocsp.entrust.net
  • Triggering command: /usr/bin/dotnet dotnet restore (dns block)
  • Triggering command: /usr/bin/dotnet dotnet restore tests/OpcScope.Tests/OpcScope.Tests.csproj (dns block)
  • Triggering command: /usr/bin/dotnet dotnet restore --no-dependencies /home/REDACTED/work/OpcScope/OpcScope/tests/OpcScope.Tests/OpcScope.Tests.csproj --packages /home/REDACTED/work/OpcScope/.codeql-scratch/dbs/csharp/working/packages /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal /p:TargetFrameworkRootPath=/home/REDACTED/work/OpcScope/.codeql-scratch/dbs/csharp/working/emptyFakeDotnetRoot /p:NetCoreTargetingPackRoot=/home/REDACTED/work/OpcScope/.codeql-scratch/dbs/csharp/working/emptyFakeDotnetRoot (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)