ifcparse: make deleting and creating instances work on RocksDB-backed files

file.remove() on a RocksDB-backed file segfaulted. Reducing it turned up
five gaps that each made editing such a file crash or silently do
nothing:

- process_deletion_inverse() decoded the v| inverse-record values as
  size_t while the serializer, register_inverse(), unregister_inverse()
  and instances_by_reference() use uint32_t, so std::find failed and
  vals.erase(end()) was undefined behaviour. It also took the DeleteRange
  end from an iterator that is invalid when the instance has no inverse
  records. Decode as uint32_t, remove every occurrence guarded on
  "found", and derive the range end from the prefix itself.
- attribute_value::size() ignored storage_model_, so every aggregate
  assignment on a RocksDB instance threw "Invalid variant index" from
  set_attribute_value(). Branch on the storage model like the sibling
  accessors and count the deserialized aggregate.
- rocks_db_file_storage::create() was a stub returning an empty handle,
  which anything creating an instance then dereferenced. Implement it
  after in_memory_file_storage::create().
- max_id_ is only initialised by the in-memory parse, so a RocksDB file
  would have handed out ids that overwrite existing instances.
  Implement the recalculate_id_counter() stub per backend and run it
  once before the first fresh_id() on RocksDB.
- byid_.erase() was a no-op: set_to_map_transformer::erase() and
  rocksdb_set_view::erase() were stubs. The deleted instance's attribute
  keys and cached handle survived, entity_names() still listed it and
  reopening the database threw. Erase deletes every key under the
  instance's prefix; the transformer forwards to it and takes an
  on-erase hook the storage uses to drop the cached handle.

root.remove_product on the first 200 products of a 61 MB model now
leaves the same surviving ids and inverse counts whether the file was
opened from SPF or converted to RocksDB.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HNrXDmR88wKPCYwGE21SyH

src/ifcparse/rocksdb_set_view.h

@@ -23,6 +23,7 @@
 #ifdef IFOPSH_WITH_ROCKSDB
 #include <rocksdb/db.h>
 #include <rocksdb/options.h>
+#include <rocksdb/write_batch.h>
 #endif
 
 #include <memory>
@@ -196,6 +197,27 @@ public:
         return iterator();
     }
 
+    // Removes the element: every key under prefix + key + "|". The prefix
+    // with its last byte incremented is the exclusive upper bound ('}'
+    // follows '|'). Returns 1 if the element existed, 0 otherwise.
+    size_t erase(const key_type& key) {
+#ifdef IFOPSH_WITH_ROCKSDB
+        if (find(key) == end()) {
+            return 0;
+        }
+        const std::string lower_bound = prefix_ + key_to_string(key) + "|";
+        std::string upper_bound = lower_bound;
+        upper_bound.back() = '}';
+        rocksdb::WriteBatch batch;
+        batch.DeleteRange(lower_bound, upper_bound);
+        db_->Write(rocksdb::WriteOptions{}, &batch);
+        return 1;
+#else
+        static_cast<void>(key);
+        return 0;
+#endif
+    }
+
     // Read-only find: returns an iterator to the element with the given key if it exists.
     iterator find(const key_type& key) const {
 #ifdef IFOPSH_WITH_ROCKSDB
@@ -216,11 +238,6 @@ public:
         return end();
     }
 
-    size_t erase(const key_type& key) {
-        static_cast<void>(key);
-        // @todo
-        return 0;
-    }
 };
 
 #endif