Add PHP Analyzer Plugin and Composer Lock Data Handling

- Implemented the PhpAnalyzerPlugin to analyze PHP projects.
- Created ComposerLockData class to represent data from composer.lock files.
- Developed ComposerLockReader to load and parse composer.lock files asynchronously.
- Introduced ComposerPackage class to encapsulate package details.
- Added PhpPackage class to represent PHP packages with metadata and evidence.
- Implemented PhpPackageCollector to gather packages from ComposerLockData.
- Created PhpLanguageAnalyzer to perform analysis and emit results.
- Added capability signals for known PHP frameworks and CMS.
- Developed unit tests for the PHP language analyzer and its components.
- Included sample composer.lock and expected output for testing.
- Updated project files for the new PHP analyzer library and tests.

src/Excititor/__Libraries/StellaOps.Excititor.Core/Observations/VexLinksetObservationRefCore.cs

@@ -0,0 +1,34 @@
+using System;
+using System.Collections.Immutable;
+
+namespace StellaOps.Excititor.Core.Observations;
+
+/// <summary>
+/// Minimal observation reference used in linkset updates while preserving Aggregation-Only semantics.
+/// </summary>
+public sealed record VexLinksetObservationRefCore(
+    string ObservationId,
+    string ProviderId,
+    string Status,
+    double? Confidence,
+    ImmutableDictionary<string, string> Attributes)
+{
+    public static VexLinksetObservationRefCore Create(
+        string observationId,
+        string providerId,
+        string status,
+        double? confidence,
+        ImmutableDictionary<string, string>? attributes = null)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(observationId);
+        ArgumentException.ThrowIfNullOrWhiteSpace(providerId);
+        ArgumentException.ThrowIfNullOrWhiteSpace(status);
+
+        return new VexLinksetObservationRefCore(
+            observationId.Trim(),
+            providerId.Trim(),
+            status.Trim(),
+            confidence,
+            attributes ?? ImmutableDictionary<string, string>.Empty);
+    }
+}