[Feature] Macros to parse Ether and other units from string to U256

### Component

primitives

### Describe the feature you would like

Often you have fixed values that could already be parsed during compile time. Currently I am initializing those values using lazy_static. My proposal would be to have macros to parse ether, wei, etc. from a string to U256.

Currently you will write:
```rust
let val: U256 = parse_units("0.01", "ether").unwrap().get_absolute();
```

Proposal:
```rust
let val: U256 = ether!("0.01");
```

If the parsing fails it will throw an error during compile time.

### Additional context

_No response_