fix(cli): gate the hashing module with the only module that uses it

`crates/cli/src/lib.rs` declares `mod update` as
`#[cfg(not(target_env = "ohos"))]`, but `mod hashing` — whose only consumer in
the crate is `update.rs` — was not gated. On the OpenHarmony target `update` is
not compiled, so `sha256_hex` has no users there and the OHOS
`cargo check` job fails under `-D warnings` with
`function sha256_hex is never used`.

Gating `hashing` exactly as its only user removes the dead item on that target
and changes nothing on any other, where both modules still compile.

Verified: `cargo check -p codewhale-cli --lib` under RUSTFLAGS="-D warnings"
passes. The OHOS target toolchain is not installed here, so the OHOS build
itself is verified only by the CI job that reported the failure.

Not established: whether this failure is older than this session's changes; the
module split that produced it predates them (`9a88b2fd88`), and the signature
is a target-gating omission rather than anything the S2 moves touched.

crates/cli/src/lib.rs

@@ -2,6 +2,7 @@
 
 mod config_bundles;
 mod credential_handoff;
+#[cfg(not(target_env = "ohos"))]
 mod hashing;
 mod metrics;
 #[cfg(not(target_env = "ohos"))]