feat(hyperhdr): vendor the flatbuffers schemas and generated bindings

The .fbs files come from HyperHDR (see schema/NOTICE); the *_generated.rs
files are flatc output regenerated by scripts/regen-fbs.sh, which refuses to
run unless flatc matches the pinned flatbuffers crate.

schema/hyperhdr_request.fbs

@@ -0,0 +1,50 @@
+// Copied verbatim from HyperHDR (https://github.com/awawa-dev/HyperHDR),
+// include/flatbuffers/parser/hyperhdr_request.fbs @ 3a76dcd (24.0.0-beta.0).
+// Copyright (c) 2020-2026 awawa-dev. MIT License, see schema/NOTICE.
+
+namespace hyperhdrnet;
+
+// A priority value of -1 clears all priorities
+table Register {
+  origin:string (required);
+  priority:int;
+}
+
+table RawImage {
+  data:[ubyte];
+  width:int = -1;
+  height:int = -1;
+}
+
+table NV12Image {
+  data_y:[ubyte];
+  data_uv:[ubyte];
+  width:int;
+  height:int;
+  stride_y:int = 0;
+  stride_uv:int = 0;
+}
+
+union ImageType {RawImage, NV12Image}
+
+table Image {
+  data:ImageType (required);
+  duration:int = -1;
+}
+
+table Clear {
+  priority:int;
+}
+
+table Color {
+  data:int = -1;
+  duration:int = -1;
+}
+
+union Command {Color, Image, Clear, Register}
+
+table Request {
+  command:Command (required);
+}
+
+root_type Request;