emberwave v0.6.0

Encoding for hosts: the encoder in the C API, with planes at any row stride and packets for the network, and in Rust from pictures that are on the GPU already, such as a screen capture's.

Added

• An encoder in the C API (#42): emberwave_encoder_create, _encode, _info and _destroy encode planes with row strides into a frame in the caller's buffer, with the colour signalling of EmberwaveSignalling, and emberwave_frame_packets splits a frame into packets for a decoder (decision D33). examples/c/encode.c shows them in use.
• gpu::Encoder::encode_strided encodes planes whose rows are a stride apart, and a stride below the width is the new EncodeError::PlaneStride.
• Encoding pictures that are on the GPU already (#33): gpu::Encoder::encode_textures takes a TexturePicture, three R8Unorm textures or NV12's layout of an R8Unorm and an Rg8Unorm texture, and makes the bytes encode makes of the same picture in CPU memory, without the CPU writing the planes (decision D32). An unsuitable texture is the new GpuError::Texture. emberwave-cli bench-encode --gpu --textures times it.

Changed

• GpuError has a new variant, Texture, and EncodeError one, PlaneStride; a match over every variant needs arms for them.
• A context asks for the adapter's largest 2D textures, as it asks for its largest buffers, so that the textures of pictures to encode can be as large as the pictures; one limited to WebGPU's guarantees keeps 8192.