fix: preserve nested XR identity during diff

[jcogilvie]

Description of your changes

Problem

When diffing XRs with nested compositions (XRs that create other XRs as composed resources), the tool incorrectly treated nested XRs as entirely new resources. This caused all managed resources owned by nested XRs to appear as removed/re-added, showing hundreds of spurious changes instead of just the actual modifications.

Root Cause: Nested XRs weren't being matched to their existing cluster instances by the crossplane.io/composition-resource-name annotation, causing identity loss during diff calculation.

Solution

1. Identity Preservation: Nested XRs are now correctly matched to existing cluster instances using their composition-resource-name annotation, preserving their cluster identity across renders
2. Composite Label Handling: Fixed handling of crossplane.io/composite labels on nested resources - these labels always point to the root XR name (empirically verified behavior), not the immediate parent
3. Namespace Filtering: Composition client now properly handles namespace filtering for cluster-scoped XRs when fetching by namespace
4. Two-Phase Diff Calculation: Separated removal detection from non-removal diffs to ensure nested XRs are processed before identifying truly removed resources
5. Test Normalization: Added normalization to E2E test golden files to strip ANSI codes and replace random generated names with placeholders, reducing test churn while maintaining colorization coverage in integration tests

Testing

• Added comprehensive E2E test coverage for nested XR scenarios (generateName and explicit names)
• Added test coverage for Claims with backing XRs

Fixes #144

I have:

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• Added or updated unit tests.
• Added or updated e2e tests.
  - [ ] Documented this change as needed.
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