Support compute_dtype for FP4/FP8 tensor core FLOPS selection

Add `compute_dtype` field to ModelConfig ("bf16", "fp8", "fp4") which
controls two things:
- GPU FLOPS tier: auto-selects from preset FP4/FP8/BF16 TFLOPS
- Weight bytes: uses 0.5/1.0/2.0 bytes per param for memory-bound check

Hardware presets now include per-GPU FP8 and FP4 dense FLOPS for all
GPUs that support them (H100/H800/H20: FP8, B200/B300: FP8+FP4).
Config resolution auto-selects the right FLOPS when compute_dtype is
set and the user hasn't explicitly overridden gpu_flops.

GLM-5-NVFP4 on 8xB300 now correctly uses 13.5 PFLOPS/GPU FP4 (6x
faster prefill) and 0.5 bytes/param weights (halved memory footprint).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/smoke.rs

@@ -22,6 +22,8 @@ fn base_config(trace_path: &str, out_dir: &str, mode: RouterMode) -> Config {
         },
         hardware: HardwareConfig {
             gpu_flops: 1.0e14,
+            gpu_fp8_flops: 0.0,
+            gpu_fp4_flops: 0.0,
             gpu_mem_bw: 1.0e12,
             hbm_bytes: 1.0e9,
             dram_bytes: 4.0e9,