feat: add repo planning/binary repo support and Meson build integration

- add repos.toml source/binary repo configuration with arch overrides and priorities
- add dependency planner/execution plan flow with interactive provider selection and --yes support
- expand binary repo DB metadata (sha512, dependencies, file lists) and repo owns/search helpers
- add rootfs-scoped fd locking and minisign detached signing/verification helpers
- add Meson build/test support for the project with builddir-local CARGO_HOME/CARGO_TARGET_DIR
- install contrib example configs into sysconfdir (/etc/depot.d layout) via Meson
- improve builder env handling (sanitized PATH, tool env passthrough, CXXFLAGS support)
- support += appends in package specs and add build.flags.cxxflags parsing
- prompt for git credentials when private repo auth is required
- update docs/examples and dependency setup (system libs, zstdmt, tempfile pin)

src/builder/python.rs

@@ -245,7 +245,7 @@ fn build_wheel_setup_py(
         .arg("bdist_wheel")
         .arg("--dist-dir")
         .arg(dist_dir);
-    crate::builder::prepare_command(&mut cmd, &env_vars.to_vec());
+    crate::builder::prepare_tool_command(&mut cmd, &env_vars.to_vec());
 
     let status = cmd
         .status()