fix(test): use direct zero-filled dictionary probe storage

Use vec![0; size] in the local-dictionary allocator probe so the focused
Rust tests satisfy the repository's strict clippy configuration. The probe
still owns the allocation until the test releases it and production code is
unchanged.

Test Plan:
- git diff --check
- ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo clippy --manifest-path rust/Cargo.toml --all-targets -- -A clippy::manual-bits -D warnings

rust/src/zstd_compress_dictionary.rs

@@ -2883,8 +2883,7 @@ mod tests {
             return ptr::null_mut();
         }
 
-        let mut allocation = Vec::<u8>::with_capacity(size);
-        allocation.resize(size, 0);
+        let mut allocation = vec![0u8; size];
         let buffer = allocation.as_mut_ptr();
         probe.allocation = buffer;
         probe.allocation_capacity = allocation.capacity();