Pin Rust toolchain to 1.94.0 via rust-toolchain.toml for deterministic
compiler output across environments. Set SOURCE_DATE_EPOCH from git
commit timestamp in CI workflows and packaging scripts to normalize
embedded timestamps.
Make packaging archives reproducible: pass --mtime=@$SOURCE_DATE_EPOCH
to tar in .deb, .ipk, and systemd tarball builds. Normalize ownership
to root:root in systemd tarballs. Pin cargo-zigbuild to 0.19.8 for
cross-compilation stability.
Add SHA-256 hash output to CI build and OpenWrt packaging workflows
for binary verification.
