[imakris]

Why

Each label fade update allocates a separate temporary vector for the previous and current text of every emitted label. Those vectors never contain more than two entries. The final prepared draw list also uses stable_sort even though its comparator ends with a unique insertion_order key.

Changes

• Store each label's two temporary text records inline, retaining the existing emission and duplicate-suppression behavior and C++17 compatibility.
• Use std::sort for the final prepared draw list. Preserve the earlier stable_sort that controls layer preparation order.

Validation

• Built test_core_algo and test_qrhi_layer_lifecycle in Release with the supplied Qt 6.12/GCC 13 SDK, text support and MSDF RHI enabled.
• CoreAlgo passed all 32 checks; QrhiLayerLifecycle passed all 40 checks, including layer preparation and final draw ordering.
• Compiled a production-header instantiation separately with -std=c++17 -pedantic-errors. The full-text build itself uses C++20 through its dependency requirements.
• git diff --check passed.

The earlier isolated allocation experiment motivated this change. End-to-end Logonomic profiling and visual validation on the deployment platforms remain outstanding; this PR does not claim an application-wide speedup.