Build a configuration-matched Cargo archive from Meson and flatten its object
members into static libzstd. This gives C consumers one archive even though
the migrated Rust objects and remaining C code refer to each other.
Shared libraries whole-archive the Cargo output to retain Rust-only ABI
exports. The implementation supports Meson 0.50's generated-archive linking
rules, matching HUF mode and 32-bit configuration, and documents cross-build
target and archiver selection.
Test Plan:
- fresh Meson both-build smoke consumers and invalidDictionaries
- modern static/shared/both, forced-HUF, i686, install, and fuzzer paths
- real Meson 0.50 static and shared smoke builds
- cargo clippy, cargo clippy --benches, cargo clippy --tests, and nightly fmt
Refs: build/meson/README.md archive and cross-build documentation
