[codex] Fix Firebase binding surface coverage false positives

[AdamEssenmacher]

Summary

• Fixes Firebase binding surface coverage false positives from shorthand source type names such as Core.App vs reflected runtime names such as Firebase.Core.App.
• Stops ApiDefinition helper/event-args exports from being treated as Objective-C class surfaces in the generated coverage inventory.
• Adds regression coverage for notification event-args helper exports so they stay reflection-only instead of native-class probes.

Root Cause

The exhaustive E2E coverage harness was stricter than the generated binding runtime shape in two places:

• Source inventory parameter names can use namespace shorthand while reflection reports fully qualified runtime type names.
• Notification event-args helper interfaces can contain [Export] metadata used by the binding generator, but they do not correspond to real Objective-C classes or writable runtime properties.

Validation

• dotnet test scripts/FirebaseBindingAudit.Tests/FirebaseBindingAudit.Tests.csproj --no-restore
  • Passed: 50/50
• tools/e2e/run-firebase-foundation.sh --package-dir output --configuration Debug --binding-surface-target all
  • Passed
  • Binding surface coverage: 1507 surfaces, 1507 exercised, 0 waived, 0 failed
• git diff --check
  • Passed

Notes

Unrelated local changes were intentionally left out of this PR: docs/firebase-runtime-failure-backlog.md and .github/workflows/firebase-e2e.yml.