Make parquet schema index type consistent (#14256)

While working on parquet schema issue I noticed that the parent and child index didn't match. Discussion ensued and `size_type` was decided.

Authors:
  - Mike Wilson (https://github.com/hyperbolic2346)

Approvers:
  - Vukasin Milovanovic (https://github.com/vuule)
  - MithunR (https://github.com/mythrocks)
  - Nghia Truong (https://github.com/ttnghia)

URL: #14256

cpp/src/io/parquet/parquet.hpp

@@ -18,6 +18,8 @@
 
 #include "parquet_common.hpp"
 
+#include <cudf/types.hpp>
+
 #include <thrust/optional.h>
 
 #include <cstdint>
@@ -152,8 +154,8 @@ struct SchemaElement {
   // The following fields are filled in later during schema initialization
   int max_definition_level = 0;
   int max_repetition_level = 0;
-  int parent_idx           = 0;
-  std::vector<size_t> children_idx;
+  size_type parent_idx     = 0;
+  std::vector<size_type> children_idx;
 
   bool operator==(SchemaElement const& other) const
   {

cpp/src/io/parquet/reader_impl_helpers.cpp

@@ -213,7 +213,7 @@ void metadata::sanitize_schema()
         // add a struct child and move this element's children to the struct
         schema_elem.converted_type  = LIST;
         schema_elem.repetition_type = OPTIONAL;
-        auto const struct_node_idx  = schema.size();
+        auto const struct_node_idx  = static_cast<size_type>(schema.size());
 
         SchemaElement struct_elem;
         struct_elem.name            = "struct_node";