Optimize handler method lookup to avoid repeated inheritance chain traversal

[Copilot]

• Initial analysis and plan
• Optimize GetAllMethodsIncludingInherited to materialize results into a list
• Validate changes with tests (all 51 tests passed)
• Final code review (no issues found)
• Security scan with CodeQL (no vulnerabilities found)
• Merge parent branch to resolve build error
• Verify build succeeds (all 110 tests passed)

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[mkholt]

@copilot the build error was resolved in the parent branch, re-merge from the parent and run the build again

[Copilot]

@copilot the build error was resolved in the parent branch, re-merge from the parent and run the build again

Merged parent branch successfully in commit 0eb476b. Build now succeeds with 0 errors and all 110 tests pass (59 in XrmPluginCore.Tests + 51 in XrmPluginCore.SourceGenerator.Tests).