feat(cli): move benchmark bridge into Rust

Move benchmark parameter normalization and dispatch into the Rust CLI archive while retaining the stable C launcher entry point. Keep compact CLI variants benchmark-free and add an explicit helpers feature for the C test generators.

Test Plan:

- cargo test --manifest-path rust/cli/Cargo.toml --no-default-features --features benchmark

- cargo test --manifest-path rust/cli/Cargo.toml --no-default-features --features helpers

- cargo clippy --manifest-path rust/cli/Cargo.toml --all-targets --no-default-features --features cli,compression,decompression,benchmark

- cargo clippy --manifest-path rust/cli/Cargo.toml --all-targets --no-default-features --features helpers

- make -B -C programs -j2 zstd zstd-small zstd-frugal

- make -B -C tests -j2 test-cli-tests

- programs/zstd -b1i1 -q

rust/cli/src/lib.rs

@@ -1,8 +1,10 @@
+#[cfg(any(feature = "benchmark", feature = "helpers"))]
 #[path = "../../src/benchfn.rs"]
 mod benchfn;
-#[cfg(feature = "cli")]
+#[cfg(all(feature = "cli", feature = "benchmark"))]
 #[path = "../../src/benchzstd.rs"]
 mod benchzstd;
+#[cfg(any(feature = "benchmark", feature = "helpers"))]
 #[path = "../../src/datagen.rs"]
 mod datagen;
 #[cfg(feature = "cli")]
@@ -11,6 +13,7 @@ mod dibio;
 #[cfg(feature = "cli")]
 #[path = "../../src/fileio_prefs.rs"]
 mod fileio_prefs;
+#[cfg(any(feature = "benchmark", feature = "helpers"))]
 #[path = "../../src/lorem.rs"]
 mod lorem;
 #[path = "../../src/timefn.rs"]