feat(bf16): remove nvrtc from entire workspace + wire ml-core precompiled cubins
- Fork cudarc locally (vendor/cudarc): add CudaContext::load_cubin()
that calls cuModuleLoadData directly — zero nvrtc dependency
- Remove "nvrtc" feature from ml-core, ml-dqn, ml-ppo Cargo.toml
- Replace all 89 Ptx::from_binary + load_module calls with load_cubin
- ml-core cuda_autograd: wire 9 stub constructors to precompiled cubins
(activation, elementwise, linear, loss, reduction, dropout, layer_norm, optimizer)
- ml-core build.rs: compile 8 BF16-native CUDA kernels via nvcc
- cubin_loader.rs: thin wrapper around CudaContext::load_cubin()
- Fix size_of::<f32> in gpu_tensor.rs, stream_ops.rs, layer_norm.rs
- Fix test data: Vec<f32> → Vec<half::bf16> for memcpy_htod
- Stub ml-ppo/ml-dqn runtime compile_ptx calls (dead code)
- backtest_metrics_kernel.cu: full native BF16 rewrite (no float)
- backtest_env_kernel.cu: shared memory → __nv_bfloat16
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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