change(rust): Use link-time optimisation in release builds (#4184)

* Move Rust optimisations to Cargo.toml

Previously they were in the Dockerfile,
so they only applied to those builds.

* Use link-time optimisation in release builds

* Retry after log ssh failures in full sync test

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Cargo.toml

@@ -51,6 +51,18 @@ opt-level = 1
 [profile.release]
 panic = "abort"
 
+# Speed up release builds and sync tests using link-time optimization.
+# Some of Zebra's code is CPU-intensive, and needs extra optimizations for peak performance.
+#
+# TODO:
+# - add "-Clinker-plugin-lto" in .cargo/config.toml to speed up release builds
+#     - add "-Clinker=clang -Clink-arg=-fuse-ld=lld" in .cargo/config.toml
+# - also use LTO on C/C++ code:
+#     - use clang to compile all C/C++ code
+#     - add "-flto=thin" to all C/C++ code builds
+#     - see https://doc.rust-lang.org/rustc/linker-plugin-lto.html#cc-code-as-a-dependency-in-rust
+lto = "thin"
+
 [patch.crates-io]
 
 # TODO: replace with upstream librustzcash when these changes are merged (#3037)

docker/Dockerfile

@@ -42,12 +42,6 @@ RUN if [ "$(uname -m)" != "aarch64" ]; then \
     && \
     rm -rf /var/lib/apt/lists/* /tmp/*
 
-# Optimize builds. In particular, regenerate-stateful-test-disks.yml was reaching the
-# GitHub Actions time limit (6 hours), so we needed to make it faster.
-#
-# TODO: apply this optimisation level to all release builds in .cargo/config.toml
-ENV RUSTFLAGS "-C opt-level=3"
-
 ENV CARGO_HOME /app/.cargo/
 # Build dependencies - this is the caching Docker layer!
 RUN cargo chef cook --release --features enable-sentry --recipe-path recipe.json