Function dispatch_kv_cache_copy 

pub fn dispatch_kv_cache_copy(
    encoder: &mut CommandEncoder,
    registry: &mut KernelRegistry,
    device: &DeviceRef,
    src: &MlxBuffer,
    cache: &MlxBuffer,
    write_pos: u32,
    row_size: u32,
    n_new: u32,
    cache_cap: u32,
    is_sliding: bool,
) -> Result<()>

Dispatch a GPU copy from a source bf16 buffer into a KV cache buffer.

Both src and cache must be bf16 Metal buffers in shared memory.

Arguments

• encoder - Command encoder to record the dispatch into.
• registry - Kernel registry (must have kv_cache_copy registered).
• device - Metal device for pipeline compilation.
• src - Source buffer of shape [n_new, row_size] (bf16).
• cache - Destination cache buffer (bf16, pre-allocated).
• write_pos - Starting write position in the cache (token index).
• row_size - Elements per token row (n_kv_heads * head_dim).
• n_new - Number of new tokens to copy.
• cache_cap - Cache capacity (window size for sliding, max_seq_len for global).
• is_sliding- Whether to use modulo wrapping (true for sliding window).

Errors

Returns MlxError::InvalidArgument if parameters are inconsistent.