Add checkpoint variant with uint256 keys and values (#5748)

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>

scripts/generate/templates/Checkpoints.opts.js

@@ -1,11 +1,12 @@
 // OPTIONS
-const VALUE_SIZES = [224, 208, 160];
+const VALUE_SIZES = [256, 224, 208, 160];
 
 const defaultOpts = size => ({
   historyTypeName: `Trace${size}`,
   checkpointTypeName: `Checkpoint${size}`,
   checkpointFieldName: '_checkpoints',
-  keyTypeName: `uint${256 - size}`,
+  checkpointSize: size < 256 ? 1 : 2,
+  keyTypeName: size < 256 ? `uint${256 - size}` : 'uint256',
   keyFieldName: '_key',
   valueTypeName: `uint${size}`,
   valueFieldName: '_value',