perf(encode/nvenc-linux): LN2 v1 — stream-ordered submit via NvEncSetIOCudaStreams

Bind the session's IO streams to the encode thread's high-priority copy
stream: in sync-retrieve depth-1 use the per-frame input copy and cursor
blend now enqueue with NO cuStreamSynchronize and encode_picture orders
after them on the stream. Same stream both directions, so the encode's
completion is inserted into the stream and later work (the next frame's
copy into a reused ring slot) waits for it.

Soundness gate: the fast path engages only when pending is empty (true
depth-1 usage) — every prior encode was drained by a blocking poll, and
the caller holds the frame payload across the matching poll (contract now
documented on Encoder::submit; both host loops already comply). Pipelined
callers and PUNKTFUNK_NVENC_ASYNC mode keep the blocking copies.

True zero-copy input registration (registering the worker-owned IPC
buffer directly) stays the LN2 v2 follow-up — it needs a contiguous
worker-pool NV12 layout and a registration<->IPC-mapping lifetime tie.

PUNKTFUNK_NVENC_STREAM_ORDERED=0 restores the old blocking behavior.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/pf-encode/src/enc/linux/mod.rs

@@ -826,7 +826,7 @@ impl NvencEncoder {
                         (*f).linesize[i] as usize,
                     )
                 });
-                pf_zerocopy::cuda::copy_yuv444_to_device(buf, dsts)
+                pf_zerocopy::cuda::copy_yuv444_to_device(buf, dsts, true)
             } else if self.want_444 {
                 ffi::av_frame_free(&mut f);
                 bail!(
@@ -839,11 +839,11 @@ impl NvencEncoder {
                 let y_pitch = (*f).linesize[0] as usize;
                 let uv_ptr = (*f).data[1] as pf_zerocopy::cuda::CUdeviceptr;
                 let uv_pitch = (*f).linesize[1] as usize;
-                pf_zerocopy::cuda::copy_nv12_to_device(buf, y_ptr, y_pitch, uv_ptr, uv_pitch)
+                pf_zerocopy::cuda::copy_nv12_to_device(buf, y_ptr, y_pitch, uv_ptr, uv_pitch, true)
             } else {
                 let dst_ptr = (*f).data[0] as pf_zerocopy::cuda::CUdeviceptr;
                 let dst_pitch = (*f).linesize[0] as usize;
-                pf_zerocopy::cuda::copy_device_to_device(buf, dst_ptr, dst_pitch)
+                pf_zerocopy::cuda::copy_device_to_device(buf, dst_ptr, dst_pitch, true)
             };
             if let Err(e) = copy_res {
                 ffi::av_frame_free(&mut f);