fix cudaErrorIllegalAddress

[gdhy9064]

Use cfg.n_rays_per_batch instead of default n_rays_per_batch 4096 in JNeRF/python/jnerf/models/position_encoders/hash_encoder/grid_encode.py which may cause cudaErrorIllegalAddress below when cfg.n_rays_per_batch much greater than 4096.

code=700( cudaErrorIllegalAddress ) cudaMemcpy(a.ptr, var->mem_ptr, var->size, cudaMemcpyDeviceToHost)

[Jittor]

Thanks!