Ensure constant host architecture when reproducibly building the wasm

Host architecture, for some reason, can effect the generated code despite the
target architecture always being foreign to the host architecture.

orchestration/runtime/Dockerfile

@@ -1,4 +1,4 @@
-FROM rust:1.75.0-slim-bookworm as builder
+FROM --platform=linux/amd64 rust:1.75.0-slim-bookworm as builder
 
 # Move to a Debian package snapshot
 RUN rm -rf /etc/apt/sources.list.d/debian.sources && \