feat(cli): port utility and dictionary I/O helpers to Rust

Move filename tables, file-list expansion, core-count helpers, statistics,
and dictionary sample loading behind Rust implementations while retaining
the narrow C ABI used by the CLI.

Test Plan:
- RUSTC_WRAPPER= CARGO_BUILD_RUSTC_WRAPPER= cargo test --manifest-path rust/cli/Cargo.toml
- RUSTC_WRAPPER= CARGO_BUILD_RUSTC_WRAPPER= cargo clippy --manifest-path rust/cli/Cargo.toml --all-targets -- -D warnings
- make -B -C programs zstd V=1
- make -C tests check V=1

rust/cli/src/lib.rs

@@ -3,12 +3,17 @@ mod benchfn;
 #[path = "../../src/datagen.rs"]
 mod datagen;
 #[cfg(feature = "cli")]
+#[path = "../../src/dibio.rs"]
+mod dibio;
+#[cfg(feature = "cli")]
 #[path = "../../src/fileio_prefs.rs"]
 mod fileio_prefs;
 #[path = "../../src/lorem.rs"]
 mod lorem;
 #[path = "../../src/timefn.rs"]
 mod timefn;
+#[path = "../../src/util.rs"]
+mod util;
 #[cfg(feature = "cli")]
 #[path = "../../src/zstd_cli.rs"]
 mod zstd_cli;