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

programs/Makefile

@@ -34,6 +34,8 @@ RUST_SOURCES := $(RUST_MANIFEST) $(RUST_DIR)/Cargo.lock \
 RUST_CLI_SOURCES := $(RUST_CLI_MANIFEST) $(RUST_CLI_DIR)/Cargo.lock \
                     $(RUST_CLI_DIR)/src/lib.rs $(RUST_DIR)/src/zstd_cli.rs \
                     $(RUST_DIR)/src/fileio_prefs.rs \
+                    $(RUST_DIR)/src/dibio.rs \
+                    $(RUST_DIR)/src/util.rs \
                     $(RUST_DIR)/src/timefn.rs $(RUST_DIR)/src/benchfn.rs \
                     $(RUST_DIR)/src/datagen.rs $(RUST_DIR)/src/lorem.rs