feat(ns): improve optimization flags and add namespaces (#1261)

Signed-off-by: k4yt3x <i@k4yt3x.com>

include/libvideo2x/libplacebo.h

@@ -7,6 +7,9 @@ extern "C" {
 #include <libavfilter/avfilter.h>
 }
 
+namespace video2x {
+namespace processors {
+
 int init_libplacebo(
     AVFilterGraph **filter_graph,
     AVFilterContext **buffersrc_ctx,
@@ -17,3 +20,6 @@ int init_libplacebo(
     uint32_t vk_device_index,
     const std::filesystem::path &shader_path
 );
+
+}  // namespace processors
+}  // namespace video2x