feat(copc): expose runtime probe tile selections

[snkmcb]

Summary:

• Add deterministic selected COPC tile identities to the runtime streaming probe.
• Report aligned point-data byte ranges for host-side comparison.
• Replace fragile TSV regex assertions with column-based CTest validation and document the output contract.

Validation:

• cmake --build build/runtime-streaming-probe-tests --config Release --target usdCopc_runtime_streaming_probe
• ctest --test-dir build/runtime-streaming-probe-tests -C Release -R '^usdCopc_(unit|runtime_streaming_probe)$' --output-on-failure
• git diff --check