## Description 

Adds `to_string` to integer modules (`u8`->`u256`)

## Test plan 

Features tests.

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## Release notes

* unsigned integers now support `.to_string()` methods, for example
`10u8.to_string()` is the same as `b"10".to_string()`

- [x] Protocol: 
- [ ] Nodes (Validators and Full nodes): 
- [ ] Indexer: 
- [ ] JSON-RPC: 
- [ ] GraphQL: 
- [ ] CLI: 
- [ ] Rust SDK:
- [ ] REST API: