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-node/src/serializer.rs

@@ -16,7 +16,7 @@
 
 //! Project (de)serialization: the C++ `ProjectSerializer` family.
 //!
-//! XML I/O goes through oakcommon's [`XmlReader`]/[`XmlWriter`] (direct
+//! XML I/O goes through oak_core's [`XmlReader`]/[`XmlWriter`] (direct
 //! Rust calls, single-lib unification). The XML shape mirrors
 //! the C++ `Node::save`/`Project::save` writers (`// CPP-PARITY:
 //! src/node/src/node.cpp:node::save`, `// CPP-PARITY:
@@ -32,7 +32,7 @@
 
 use std::sync::{Arc, Mutex};
 
-use oak_common::xmlutils::{XmlReader, XmlWriter};
+use oak_core::xmlutils::{XmlReader, XmlWriter};
 use oak_core::Rational;
 
 use crate::graph::Graph;
@@ -43,7 +43,7 @@ use crate::project::{NodeRef, Project};
 use crate::value::{NodeValue, ValueType};
 
 /// Minimal XML reader surface the serializer needs (implemented over
-/// oakcommon's `xmlutils`).
+/// oak_core's `xmlutils`).
 pub trait XmlRead {
 	/// Advance to the next start element; false at end/close.
 	fn next_start_element(&mut self) -> bool;
@@ -73,17 +73,17 @@ pub trait XmlWrite {
 	fn characters(&mut self, _text: &str) {}
 }
 
-/// Reader over oakcommon's [`XmlReader`].
+/// Reader over oak_core's [`XmlReader`].
 pub struct XmlReaderBridge {
-	/// The oakcommon reader.
+	/// The oak_core reader.
 	reader: XmlReader,
 	/// Current element name (cached).
 	name: String,
 }
 
-/// Writer over oakcommon's [`XmlWriter`].
+/// Writer over oak_core's [`XmlWriter`].
 pub struct XmlWriterBridge {
-	/// The oakcommon writer.
+	/// The oak_core writer.
 	writer: XmlWriter,
 }
 
@@ -277,7 +277,7 @@ pub fn parse_node_ref(text: &str) -> Option<NodeId> {
 pub fn save(project: &Project) -> crate::error::Result<String> {
 	use crate::error::Error;
 	let mut writer = XmlWriterBridge::new().ok_or(Error::Failed(
-		"oakcommon XML writer unavailable".to_string(),
+		"oak_core XML writer unavailable".to_string(),
 	))?;
 
 	writer.start_element("project");
@@ -510,7 +510,7 @@ pub fn load_with_id_map(
 ) -> crate::error::Result<(Arc<Mutex<Project>>, std::collections::HashMap<u64, NodeId>)> {
 	use crate::error::Error;
 	let mut reader = XmlReaderBridge::new(xml).ok_or(Error::Failed(
-		"oakcommon XML reader unavailable".to_string(),
+		"oak_core XML reader unavailable".to_string(),
 	))?;
 
 	// Detect the root element.