refactor(compress): move heap CCtx release order to Rust

ZSTD_freeCCtx previously passed one C callback that bundled dictionary,
multithreaded context, workspace, and heap-object teardown. That left the
lifetime order inside private C control flow and made the public destruction
policy harder to audit. Project the four private operations separately and
let Rust enforce the original dictionary, MT-context, workspace, and
object order while preserving the static-context and workspace-embedded
object guards. The callbacks still own the C layouts and custom allocator
operations.

Test Plan:
- `ulimit -v 41943040; cargo +nightly fmt --manifest-path rust/Cargo.toml --all -- --check` -- passed
- `ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo clippy --manifest-path rust/Cargo.toml --all-targets -- -D warnings` -- passed
- Broader native and original-test verification remains pending for the complete batch.

rust/src/zstd_compress.rs

@@ -2550,34 +2550,38 @@ pub unsafe extern "C" fn ZSTD_rust_initStaticCCtx(
     }
 }
 
-type FreeCCtxContentFn = unsafe extern "C" fn(*mut c_void);
-type FreeCCtxObjectFn = unsafe extern "C" fn(*mut c_void);
+type FreeCCtxCallbackFn = unsafe extern "C" fn(*mut c_void);
 
 /// Explicit projection for the public `ZSTD_freeCCtx` wrapper.
 ///
-/// Rust owns the null/static/embedded-object policy and callback ordering.
-/// C retains the private content teardown and custom allocator callbacks.
+/// Rust owns the null/static/embedded-object policy and the release order.
+/// C retains only the private dictionary, MT-context, workspace, and custom
+/// allocator operations behind narrow callbacks.
 #[repr(C)]
 pub struct ZSTD_rust_freeCCtxState {
     callback_context: *mut c_void,
     static_size: usize,
     cctx_in_workspace: c_int,
-    free_content: FreeCCtxContentFn,
-    free_object: FreeCCtxObjectFn,
+    free_dictionaries: FreeCCtxCallbackFn,
+    free_mt_context: FreeCCtxCallbackFn,
+    free_workspace: FreeCCtxCallbackFn,
+    free_object: FreeCCtxCallbackFn,
 }
 
 const _: () = {
-    assert!(size_of::<FreeCCtxContentFn>() == size_of::<usize>());
-    assert!(size_of::<FreeCCtxObjectFn>() == size_of::<usize>());
+    assert!(size_of::<FreeCCtxCallbackFn>() == size_of::<usize>());
     assert!(offset_of!(ZSTD_rust_freeCCtxState, callback_context) == 0);
     assert!(offset_of!(ZSTD_rust_freeCCtxState, static_size) == size_of::<usize>());
     assert!(offset_of!(ZSTD_rust_freeCCtxState, cctx_in_workspace) == 2 * size_of::<usize>());
-    assert!(offset_of!(ZSTD_rust_freeCCtxState, free_content) == 3 * size_of::<usize>());
-    assert!(offset_of!(ZSTD_rust_freeCCtxState, free_object) == 4 * size_of::<usize>());
-    assert!(size_of::<ZSTD_rust_freeCCtxState>() == 5 * size_of::<usize>());
+    assert!(offset_of!(ZSTD_rust_freeCCtxState, free_dictionaries) == 3 * size_of::<usize>());
+    assert!(offset_of!(ZSTD_rust_freeCCtxState, free_mt_context) == 4 * size_of::<usize>());
+    assert!(offset_of!(ZSTD_rust_freeCCtxState, free_workspace) == 5 * size_of::<usize>());
+    assert!(offset_of!(ZSTD_rust_freeCCtxState, free_object) == 6 * size_of::<usize>());
+    assert!(size_of::<ZSTD_rust_freeCCtxState>() == 7 * size_of::<usize>());
 };
 
-/// Free the C-owned context content and, when applicable, its outer object.
+/// Release a heap CCtx in the original dictionary, MT-context, workspace, and
+/// outer-object order.
 #[no_mangle]
 pub unsafe extern "C" fn ZSTD_rust_freeCCtx(state: *const ZSTD_rust_freeCCtxState) -> usize {
     if state.is_null() {
@@ -2591,7 +2595,9 @@ pub unsafe extern "C" fn ZSTD_rust_freeCCtx(state: *const ZSTD_rust_freeCCtxStat
         return ERROR(ZstdErrorCode::MemoryAllocation);
     }
     unsafe {
-        (state.free_content)(state.callback_context);
+        (state.free_dictionaries)(state.callback_context);
+        (state.free_mt_context)(state.callback_context);
+        (state.free_workspace)(state.callback_context);
         if state.cctx_in_workspace == 0 {
             (state.free_object)(state.callback_context);
         }
@@ -19025,9 +19031,19 @@ mod tests {
         events: Vec<&'static str>,
     }
 
-    unsafe extern "C" fn free_cctx_test_content(context: *mut c_void) {
+    unsafe extern "C" fn free_cctx_test_dictionaries(context: *mut c_void) {
         let context = unsafe { &mut *context.cast::<FreeCCtxTestContext>() };
-        context.events.push("content");
+        context.events.push("dictionaries");
+    }
+
+    unsafe extern "C" fn free_cctx_test_mt_context(context: *mut c_void) {
+        let context = unsafe { &mut *context.cast::<FreeCCtxTestContext>() };
+        context.events.push("mt-context");
+    }
+
+    unsafe extern "C" fn free_cctx_test_workspace(context: *mut c_void) {
+        let context = unsafe { &mut *context.cast::<FreeCCtxTestContext>() };
+        context.events.push("workspace");
     }
 
     unsafe extern "C" fn free_cctx_test_object(context: *mut c_void) {
@@ -19044,20 +19060,25 @@ mod tests {
             callback_context: context,
             static_size,
             cctx_in_workspace,
-            free_content: free_cctx_test_content,
+            free_dictionaries: free_cctx_test_dictionaries,
+            free_mt_context: free_cctx_test_mt_context,
+            free_workspace: free_cctx_test_workspace,
             free_object: free_cctx_test_object,
         }
     }
 
     #[test]
-    fn free_cctx_frees_content_before_an_external_object() {
+    fn free_cctx_releases_dictionaries_mt_context_and_workspace_before_object() {
         let mut context = FreeCCtxTestContext::default();
         let state = free_cctx_test_state((&mut context as *mut FreeCCtxTestContext).cast(), 0, 0);
 
         let result = unsafe { ZSTD_rust_freeCCtx(&state) };
 
         assert_eq!(result, 0);
-        assert_eq!(context.events, ["content", "object"]);
+        assert_eq!(
+            context.events,
+            ["dictionaries", "mt-context", "workspace", "object"]
+        );
     }
 
     #[test]
@@ -19068,7 +19089,7 @@ mod tests {
         let result = unsafe { ZSTD_rust_freeCCtx(&state) };
 
         assert_eq!(result, 0);
-        assert_eq!(context.events, ["content"]);
+        assert_eq!(context.events, ["dictionaries", "mt-context", "workspace"]);
     }
 
     #[test]