fixup! Add snapshot file format design doc

Author: ludfjig

docs/snapshot-file-implementation-plan.md

@@ -303,7 +303,6 @@ snapshots since it touches the entire memory blob.
 - **Fuzz target**: Fuzz `from_file` with arbitrary bytes
 - **CLI tool**: `hl snap bake?`
 - **CoW overlay layers**
-- **Heap grow-only append**
 - **Cross-hypervisor snapshot portability**: The `hypervisor_tag`
   rejects cross-hypervisor loads because segment register hidden-cache
   fields differ between KVM, MSHV, and WHP. Could potentially be