Nitwit Stable Performance 1.2.5 - Stability Fix

Changes
- Fixes FPS frame-budget detection for invalid, zero, negative, and unlimited frame caps. These cases now use a conservative 60-FPS budget instead of potentially allowing a 250 ms frame budget.
- Stability-first defaults: render-distance reduction up to 16 chunks, minimum render distance 4, overload response after 20 sustained frames, and slow 300-frame recovery to reduce setting oscillation.
- Untouched default configurations from schema 4 are migrated automatically. Customized configurations are preserved.
- Diagnostics remain off by default to avoid unnecessary log noise.
- Keeps simulation-distance adaptation limited to an integrated single-player server; it does not attempt to control a remote server's simulation distance.
- Retains the existing Fabric world-render event sampler and existing compatibility range (Minecraft 26.0–26.3, Fabric Loader >= 0.18.4, Java >= 25).

Important limitations
- A client mod cannot guarantee a fixed FPS, eliminate input latency, increase a remote server's TPS, reduce internet ping, or control GPU/CPU thread scheduling across every mod. Results depend on hardware, drivers, renderer, other mods, and the server's workload.
- If performance does not improve, use a lower manual render distance and check server TPS/MSPT plus the client latest.log. This mod does not remove custom mobs, particles, structures, or world-generation content.
