feat: RegisterTable support for InMemoryCatalog

Author: shuxu.li

src/iceberg/catalog.h

@@ -166,7 +166,7 @@ class ICEBERG_EXPORT Catalog {
   /// \param identifier a table identifier
   /// \return instance of Table implementation referred to by identifier or
   /// ErrorKind::kNoSuchTable if the table does not exist
-  virtual Result<std::shared_ptr<Table>> LoadTable(const TableIdentifier& identifier) = 0;
+  virtual Result<std::unique_ptr<Table>> LoadTable(const TableIdentifier& identifier) = 0;
 
   /// \brief Register a table with the catalog if it does not exist
   ///

src/iceberg/catalog/in_memory_catalog.cc

@@ -408,7 +408,7 @@ Status InMemoryCatalog::DropTable(const TableIdentifier& identifier, bool purge)
   return root_namespace_->UnregisterTable(identifier);
 }
 
-Result<std::shared_ptr<Table>> InMemoryCatalog::LoadTable(
+Result<std::unique_ptr<Table>> InMemoryCatalog::LoadTable(
     const TableIdentifier& identifier) {
   if (!file_io_) [[unlikely]] {
     return InvalidArgument("file_io is not set for catalog {}", catalog_name_);
@@ -424,7 +424,7 @@ Result<std::shared_ptr<Table>> InMemoryCatalog::LoadTable(
   ICEBERG_ASSIGN_OR_RAISE(auto metadata,
                           TableMetadataUtil::Read(*file_io_, metadata_location.value()));
 
-  return std::make_shared<Table>(identifier, std::move(metadata),
+  return std::make_unique<Table>(identifier, std::move(metadata),
                                  metadata_location.value(), file_io_,
                                  std::static_pointer_cast<Catalog>(shared_from_this()));
 }

src/iceberg/catalog/in_memory_catalog.h

@@ -84,7 +84,7 @@ class ICEBERG_EXPORT InMemoryCatalog
 
   Status DropTable(const TableIdentifier& identifier, bool purge) override;
 
-  Result<std::shared_ptr<Table>> LoadTable(const TableIdentifier& identifier) override;
+  Result<std::unique_ptr<Table>> LoadTable(const TableIdentifier& identifier) override;
 
   Result<std::shared_ptr<Table>> RegisterTable(
       const TableIdentifier& identifier,