fix(mt): pass copied job projection by value

The new MT compression-job begin entry point already copied the nullable ABI projection with as_ref().copied(), but the integration call retained an unnecessary dereference. Pass the copied projection directly so the production entry point compiles under all-target clippy without changing its callback policy.

Test Plan:

- ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo clippy --manifest-path rust/Cargo.toml --all-targets -- -D warnings

- git diff --cached --check

rust/src/zstdmt_compress.rs

@@ -359,7 +359,7 @@ pub unsafe extern "C" fn ZSTDMT_rust_compressionJobBegin(
     };
 
     begin_compression_job_with(
-        *projection,
+        projection,
         || unsafe { begin_with_cdict(opaque) },
         |value| unsafe { set_force_max_window(opaque, value) },
         || unsafe { set_deterministic_ref_prefix(opaque) },