Merge branch 'ps/rust-balloon' into ps/ci-rust

* ps/rust-balloon: ci: enable Rust for breaking-changes jobs ci: convert "pedantic" job into full build with breaking changes BreakingChanges: announce Rust becoming mandatory varint: reimplement as test balloon for Rust varint: use explicit width for integers help: report on whether or not Rust is enabled Makefile: introduce infrastructure to build internal Rust library Makefile: reorder sources after includes meson: add infrastructure to build internal Rust library