Add new packages and build scripts for various libraries

- Added Nuklear GUI library with build script and configuration.
- Introduced OpenH264 encoder/decoder with build configuration.
- Added PortAudio library for audio I/O with custom build script.
- Included Python Execnet for multi-Python deployment.
- Added Pytest Xdist plugin for distributed testing.
- Introduced Shaderc for shader compilation tools.
- Added Snappy compression library with necessary patches and configuration.
- Included SoundTouch audio processing library with build configuration.
- Added SRT library for secure reliable transport.
- Introduced VapourSynth video processing framework with configuration.
- Added Vid.stab for video stabilization.
- Included WebRTC Audio Processing library with build configuration.
- Added X264 video encoding library with patches for POSIX compliance.
- Introduced X265 video encoder with build configuration.
- Added XKeyboard Config for X keyboard configuration files.
- Included Xorg XKBComp for keyboard description compilation.
- Added Xvidcore MPEG-4 video codec library with configuration.
- Introduced ZeroMQ messaging system with patches and build configuration.
- Added Zimg library for scaling and colorspace conversion.

extra/libplacebo/libplacebo.toml

@@ -0,0 +1,57 @@
+[build]
+type = "meson"
+
+[build.flags]
+build_dir = "build"
+configure = [
+    "-Dtests=true",
+    "-Dvulkan=enabled",
+    "-Dglslang=enabled",
+    "-Dshaderc=enabled",
+    "-Dlcms=enabled",
+    "-Dd3d11=disabled",
+    "-Dlibdovi=enabled",
+    "-Ddemos=false",
+]
+cxxflags += [ "-I/usr/include/glslang" ]
+skip_tests = true # need a graphical env
+
+[dependencies]
+build = [
+    "meson",
+    "vulkan-headers",
+    "glad",
+    "nuklear",
+    "python",
+    "python-setuptools",
+    "python-mako",
+    "python-markupsafe",
+    "python-jinja",
+    "libglvnd",
+]
+runtime = [
+    "vulkan-icd-loader",
+    "glslang",
+    "lcms2",
+    "shaderc",
+    "glibc",
+    "libunwind",
+    "libcxx",
+    "libdovi",
+    "xxhash",
+]
+
+[[manual_sources]]
+file = "fix_glslang_linking.patch"
+
+[package]
+description = "Reusable library for GPU-accelerated video/image rendering primitives"
+homepage = "https://github.com/haasn/libplacebo"
+license = "LGPL-2.1-or-later"
+name = "libplacebo"
+version = "7.360.1"
+
+[[source]]
+extract_dir = "$name-$version"
+patches = ["fix_glslang_linking.patch"]
+url = "https://code.videolan.org/videolan/libplacebo.git#v$version"