Re-add upload texture

[Firestar99]

Effectively just 3 commits without dependent PRs:

• dd380f9 vello: code cleanup of resource overwrites
• 45596c0 upload_texture: upload cpu textures as SRGBA8
• df9e2e1 vello: fix wgpu::Texture leak within vello's context.resource_overrides HashMap

Texture upload node

TLDR: With @TrueDoctor we decided that SRGB8 for now is fine, but we would like to switch to f32 later and add a conversion step down to SRGB8 before we give it to vello.

We would like to have linear f32 textures, as discussed with @TrueDoctor. However, this implementation currently uses Rgba8UnormSrgb converted to with graphite's SRGB8 struct, as using Rgba32Float causes FF nightly to emit Uncaptured WebGPU error: In a pass parameter, caused by: Encoder is invalid. The real fun will be debugging that, since wgpu documents the error like this:

/// Used internally by wgpu functions to indicate the encoder already
/// contained an error. This variant should usually not be seen by users of
/// the API, since an effort should be made to provide the caller with a
/// more specific reason for the encoder being invalid.
#[error("Encoder is invalid")]
Invalid,

https://github.com/gfx-rs/wgpu/blob/9b966bf8a39b07bfc495fb43e8bf7725c5df440c/wgpu-core/src/command/mod.rs#L971-L976

In other words, I have no clue to go on what's going wrong. Changing the image format shouldn't have triggered anything really. The only thing I can think of is the image format being unsupported for sampling, I'd have to verify this later. At least vulkan says I very much can with my hardware.