fix(windows): vendor audiopus_sys + patch libopus for clang-cl SIMD

cargo-xwin drives the Windows MSVC cross-compile via clang-cl, under
which CMake sets MSVC=1 — causing libopus 1.3.1's `if(NOT MSVC)` guards
to skip the per-file `-msse4.1` / `-mssse3` COMPILE_FLAGS that its x86
SIMD source files need. Clang-cl (unlike real cl.exe) still honors
Clang's target-feature system, so those files then fail to compile
with "always_inline function '_mm_cvtepi16_epi32' requires target
feature 'sse4.1'" errors across silk/NSQ_sse4_1.c, NSQ_del_dec_sse4_1.c,
and VQ_WMat_EC_sse4_1.c.

Earlier attempts to fix this downstream (cargo-xwin toolchain file,
override.cmake CMAKE_C_COMPILE_OBJECT <FLAGS> replace, CFLAGS env vars)
all failed because cargo-xwin rewrites override.cmake from scratch on
every `cargo xwin build` invocation and cmake-rs's -DCMAKE_C_FLAGS=
assembly happens before toolchain FORCE sets propagate.

Fixing it upstream at the source: vendor audiopus_sys 0.2.2 into
vendor/audiopus_sys, patch its bundled opus/CMakeLists.txt to introduce
an MSVC_CL var (true only when CMAKE_C_COMPILER_ID == "MSVC", i.e. real
cl.exe), and flip the eight `if(NOT MSVC)` SIMD guards to
`if(NOT MSVC_CL)`. Clang-cl then gets the GCC-style per-file flags and
the SSE4.1 sources build cleanly. Also flip the `if(MSVC)` global /arch
block at line 445 to `if(MSVC_CL)` so only cl.exe applies /arch:AVX and
clang-cl relies purely on per-file flags (no global/per-file mixing).

Wire via [patch.crates-io] in the workspace root Cargo.toml; the patch
is resolved relative to the workspace root as `vendor/audiopus_sys`.

Upstream context: xiph/opus#256, xiph/opus PR #257 (both stale).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/audiopus_sys/opus/update_version

@@ -0,0 +1,65 @@
+#!/bin/bash
+
+# Creates and updates the package_version information used by configure.ac
+# (or other makefiles).  When run inside a git repository it will use the
+# version information that can be queried from it unless AUTO_UPDATE is set
+# to 'no'.  If no version is currently known it will be set to 'unknown'.
+#
+# If called with the argument 'release', the PACKAGE_VERSION will be updated
+# even if AUTO_UPDATE=no, but the value of AUTO_UPDATE shall be preserved.
+# This is used to force a version update whenever `make dist` is run.
+#
+# The exit status is 1 if package_version is not modified, else 0 is returned.
+#
+# This script should NOT be included in distributed tarballs, because if a
+# parent directory contains a git repository we do not want to accidentally
+# retrieve the version information from it instead.  Tarballs should ship
+# with only the package_version file.
+#
+# Ron <ron@debian.org>, 2012.
+
+SRCDIR=$(dirname $0)
+
+if [ -e "$SRCDIR/package_version" ]; then
+    . "$SRCDIR/package_version"
+fi
+
+if [ "$AUTO_UPDATE" = no ]; then
+    [ "$1" = release ] || exit 1
+else
+    AUTO_UPDATE=yes
+fi
+
+# We run `git status` before describe here to ensure that we don't get a false
+# -dirty from files that have been touched but are not actually altered in the
+# working dir.
+GIT_VERSION=$(cd "$SRCDIR" && git status > /dev/null 2>&1 \
+                           && git describe --tags --match 'v*' --dirty 2> /dev/null)
+GIT_VERSION=${GIT_VERSION#v}
+
+if [ -n "$GIT_VERSION" ]; then
+
+    [ "$GIT_VERSION" != "$PACKAGE_VERSION" ] || exit 1
+    PACKAGE_VERSION="$GIT_VERSION"
+
+elif [ -z "$PACKAGE_VERSION" ]; then
+    # No current package_version and no git ...
+    # We really shouldn't ever get here, because this script should only be
+    # included in the git repository, and should usually be export-ignored.
+    PACKAGE_VERSION="unknown"
+else
+    exit 1
+fi
+
+cat > "$SRCDIR/package_version" <<-EOF
+	# Automatically generated by update_version.
+	# This file may be sourced into a shell script or makefile.
+
+	# Set this to 'no' if you do not wish the version information
+	# to be checked and updated for every build.  Most people will
+	# never want to change this, it is an option for developers
+	# making frequent changes that they know will not be released.
+	AUTO_UPDATE=$AUTO_UPDATE
+
+	PACKAGE_VERSION="$PACKAGE_VERSION"
+EOF