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/xvidcore/xvidcore.toml

@@ -0,0 +1,21 @@
+[build]
+type = "autotools"
+
+[build.flags]
+source_subdir = "xvidcore/build/generic"
+
+[dependencies]
+build = ["nasm"]
+runtime = ["glibc"]
+
+[package]
+description = "XviD is an open source MPEG-4 video codec"
+homepage = "https://www.xvid.com/"
+license = "GPL-2.0-or-Later"
+name = "xvidcore"
+version = "1.3.7"
+
+[[source]]
+extract_dir = "$name-$version"
+sha256 = "aeeaae952d4db395249839a3bd03841d6844843f5a4f84c271ff88f7aa1acff7"
+url = "https://downloads.xvid.com/downloads/xvidcore-$version.tar.bz2"