[BUG] Update rust SDK references `Balance` -> `NearToken`

[PiVortex]

What?

The new version of our Rust SDK (v5.0.0) deprecated the use of Balance as an import and now uses NearToken. Please update all references of this to use the correct variable.

Why?

Reference material is outdated and no longer valid

Acceptance Criteria

### Tasks
- [ ] Search docs for all references to `Balance` when using rust SDK
- [ ] Replace with `NearToken`
- [ ] TEST! To ensure they work :) 

Resources

Example -> Transfers and Actions page uses the type Balance. This is no longer a valid type and should be updated to NearToken