style: enable fmt linting for grouped imports by std external and crates

[KolbyML]

What was wrong?

We don't have the fmt linting option for the import format we all use.

The format we normally use as a team is

-1 std imports grouped up
-2 external imports grouped up
-3 crates imports grouped up

How was it fixed?

It turns out fmt has a flag for enabling this formatting so I enabled the lint option in rustfmt.toml

[morph-dev]

Rubber stamp approval (checked dozens of files and they look fine).

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Sidenote: Our trin book page says that groups should be:

• Imports from 'std'
• Imports from external crates
• Imports from crates within trin

I think this can be interpreted that other trin crates should be imported inside 3rd group, something like this:

// e.g. inside trin-storage/src
use alloy::{...};

use crate::{..};
use ethportal_api::{..};

But in reality, ethportal_api would be considered external crate, and be part of the 2nd group.

I think that we can't setup linter to do the above, so maybe while you are at it, can you update docs page to clarify.