[codex] optimize PSP stats text rendering

[doodlewind]

Summary

Optimizes the stats demo text path on PSP by moving native glyph rendering from per-frame coverage-run rect generation to cached PSM_4444 font atlas textures, then drawing each glyph as a textured sprite.

Also reduces avoidable layout churn for changing text:

• skips relayout when a text update measures to the same layout size;
• quantizes the stats demo count-up text updates to every 8 frames;
• adds scripts/bench-ppsspp.ts plus scripts/psp.ts --bench for repeatable PPSSPP timing runs.

Root Cause

The stats demo updates large numeric text every frame. On PSP this forced expensive text/layout work and the GE backend rebuilt anti-aliased glyphs by scanning coverage cells into many horizontal rect sprites each frame.

Benchmark

PPSSPP stats window, same input/window as PR #6 style benchmark:

• before: avg_work_us=38449, avg_render_us=10138, avg_tick_us=15337
• after: avg_work_us=16385, avg_render_us=1028, avg_tick_us=2666

Final 5-sample report: dist/bench/ppsspp-bench-2026-07-05T00-27-50-289Z.json locally.

Validation

• git diff --check
• bunx tsc --noEmit
• bun run test
• cargo test --manifest-path core/Cargo.toml
• PSP_SDK=/Users/evan/code/dreamcart/mipsel-sony-psp E2E_PPSSPP_TIMEOUT=60 UPDATE=1 bun test/e2e-ppsspp.ts
• PSP_SDK=/Users/evan/code/dreamcart/mipsel-sony-psp E2E_PPSSPP_TIMEOUT=60 bun test/e2e-ppsspp.ts
• PSP_SDK=/Users/evan/code/dreamcart/mipsel-sony-psp BENCH_PPSSPP_TIMEOUT=60 bun scripts/bench-ppsspp.ts --apps=stats --samples=5 --timeout=60

Post-rebase smoke:

• git diff --check
• bunx tsc --noEmit && bun run test
• PSP_SDK=/Users/evan/code/dreamcart/mipsel-sony-psp BENCH_PPSSPP_TIMEOUT=60 bun scripts/bench-ppsspp.ts --apps=stats --samples=1 --timeout=60