Zed's bundled rust-analyzer calls `cargo metadata --lockfile-path`,
which is still gated behind `-Z unstable-options` on cargo 1.95.0
(both stable and the esp Xtensa fork). Workspaces fail to load with
the bundled binary.
Point lsp.rust-analyzer.binary.path at the rustup-managed
rust-analyzer (version-locked to cargo 1.95 stable, no unstable
flags). Also set cargo.target = xtensa-esp32s3-espidf with
allTargets=false so RA doesn't try to check the crate for the host
target — esp-idf-sys can't build for macOS.
