fix: make into_raw methods private to match private return types

pub(crate) still triggers private_interfaces lint since the return
types (RawSerializable, DispatchResponseWrapper) are module-private.
These methods are only used within crdtp.rs, so make them fully private.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: bartlomieju

src/crdtp.rs

@@ -182,7 +182,7 @@ impl Serializable {
     }
   }
 
-  pub(crate) fn into_raw(self) -> *mut RawSerializable {
+  fn into_raw(self) -> *mut RawSerializable {
     let ptr = self.ptr;
     std::mem::forget(self);
     ptr
@@ -361,7 +361,7 @@ impl DispatchResponse {
     }
   }
 
-  pub(crate) fn into_raw(self) -> *mut DispatchResponseWrapper {
+  fn into_raw(self) -> *mut DispatchResponseWrapper {
     let ptr = self.ptr;
     std::mem::forget(self);
     ptr