core: merge oak-common into oak-core

oak-common is gone; its modules (configstore, xmlutils, ocioutils,
oiioutils, colormath, colortransform, videoparams, ffmpegutils, ...)
now live in oak-core alongside the value types. The render value/GPU
types moved too: backend (wgpu context + DisplayRenderer), color
(ColorProcessor over ocio-rs), texture, frame, and the commonutil
config helpers.

Fix-ups to make the merged tree build and pass tests:

- oak-core Cargo.toml: wgpu back to 25 (the moved backend code is
  written against that API generation); add the toml/quick-xml/image
  deps oak-common carried.
- lib.rs: drop the duplicate 'pub mod error;'.
- error.rs: unified OAKCORE_* codes; restore Error::new() and
  From<OcioError> from oak-common's error type.
- backend.rs/color.rs: oak_core::/oak_render:: self-references
  rewritten to crate::; the shaderfx-dependent GPU effect test moved
  to oak-render's shaderfx tests (shaderfx depends on oak-node and
  cannot live in oak-core).
- oak-render's error module re-exports oak_core::error::{Error,
  Result}; the OAKRENDER_* codes stay as the public-code contract.
- oak-node jobs.rs: ColorProcessor imported from oak_core::color.
- Integration tests repointed at oak_core::{texture, frame, backend,
  color, colormath}.
- the display-ICC regression test treats an empty OAK_DISPLAY_ICC as
  unset, matching displayicc::env_override_icc.

crates/oak-task/src/precache.rs

@@ -32,7 +32,7 @@
 //!
 //! CPP-PARITY: src/task/src/precache/precachetask.h
 
-use oak_common::videoparams::VideoParams;
+use oak_core::videoparams::VideoParams;
 
 use crate::error::Result;
 use crate::nodeops::{self, NodeRef};
@@ -114,7 +114,7 @@ impl TaskBehavior for PreCacheTask {
 }
 
 impl RenderTaskBehavior for PreCacheTask {
-	fn frame_downloaded(&mut self, task: &mut Task, frame: &oak_render::texture::Texture) -> Result<()> {
+	fn frame_downloaded(&mut self, task: &mut Task, frame: &oak_core::texture::Texture) -> Result<()> {
 		// Do nothing: pre-cache just fills the frame cache (the direct
 		// ticket arena records the render through the ticket's cache
 		// identity; see the module docs).