feat: metadata access support for table

Author: shuxu.li

src/iceberg/table.h

@@ -107,11 +107,12 @@ class ICEBERG_EXPORT Table {
 
  private:
   const TableIdentifier identifier_;
-  const std::shared_ptr<TableMetadata> metadata_;
+  std::shared_ptr<TableMetadata> metadata_;
   const std::string metadata_location_;
   std::shared_ptr<FileIO> io_;
   std::shared_ptr<Catalog> catalog_;
 
+  // Cache lazy-initialized maps.
   mutable std::shared_ptr<std::unordered_map<int32_t, std::shared_ptr<Schema>>>
       schemas_map_;
   mutable std::shared_ptr<std::unordered_map<int32_t, std::shared_ptr<PartitionSpec>>>

src/iceberg/table_metadata.h

@@ -23,14 +23,12 @@
 /// Table metadata for Iceberg tables.
 
 #include <memory>
-#include <mutex>
 #include <string>
 #include <string_view>
 #include <unordered_map>
 #include <vector>
 
 #include "iceberg/iceberg_export.h"
-#include "iceberg/snapshot.h"
 #include "iceberg/type_fwd.h"
 #include "iceberg/util/timepoint.h"