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-codec/src/decoder.rs

@@ -26,7 +26,7 @@
 use std::path::Path;
 use std::sync::{Arc, Mutex, OnceLock};
 
-use oak_common::cancelatom::CancelAtom;
+use oak_core::cancelatom::CancelAtom;
 use oak_core::{Rational, TimeRange};
 
 use crate::footagedescription::FootageDescription;
@@ -113,7 +113,7 @@ pub enum RenderMode {
 
 /// "Don't force a color range" sentinel for
 /// [`RetrieveVideoParams::force_range`] (the actual ranges are the
-/// `OAKCOMMON_COLOR_RANGE_*` values).
+/// `oak_core_COLOR_RANGE_*` values).
 pub const K_COLOR_RANGE_DEFAULT: i32 = -1;
 
 /// `Decoder::RetrieveVideoParams` — what a video retrieve call needs.