[GraphQL/Cursor] GenesisTransaction.objects (MystenLabs#15475)

## Description

Yet more Cursor framework applications -- obfuscates cursors,
standardises handling of max and default page sizes.

## Test Plan

```
sui-graphql-e2e-tests$ cargo nextest run \
  -j 1 --feature pg_integration          \
  -- system.move
```

## Stack
- MystenLabs#15467 
- MystenLabs#15470 
- MystenLabs#15471 
- MystenLabs#15472 
- MystenLabs#15473
- MystenLabs#15474