Nitwit 1.2.8 — Low-Overhead Stability

Changes:
- Disabled the reflective world-render frame sampler to remove recurring per-frame instrumentation.
- Disabled tick timing measurement and telemetry work; this build no longer reports client/server tick windows.
- Kept the lightweight client tick callback for conservative memory-pressure-based entity/particle adaptation.
- Kept the corrected PNG mod icon at assets/nitwit/icon.png.
- Updated metadata/version string only; Minecraft 1.21–26.3 is a declared compatibility target, not a claim of live testing on every version.

Important: this build is intended to isolate whether Nitwit's measurement hooks add overhead. It cannot reproduce Sodium's renderer-level optimizations, guarantee high FPS, fix remote-server TPS/ping, or make packets/hitbox changes undetectable. No custom worker threads were present in 1.2.7.
