feat: add --check option to nargo fmt for dry-run formatting verification

[ghost]

Description

❯ cargo r -- fmt --check
Differences (-original|+formatted):
 fn main() {
     let _callStackItem3 = context.call_private_function(
-        
         inputs.call_context.storage_contract_address,
         get_note_zero_fn_selector,
         [owner]
     );


❯ echo $?
1

❯ cargo r -- fmt --check
No formatting changes were detected

❯ echo $?
0

Problem

Resolves #3520

Additional Context

Documentation

Check one:

• No documentation needed.
• Documentation included in this PR.
• [Exceptional Case] Documentation to be submitted in a separate PR.

PR Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[kevaundray]

Invisible differences: the two values are the same in string form.

If this is the output when there are no formatting changes, we should change it to something like: "No formatting changes were detected" which is eaiser to read for me.

Prettier says something like "All matched files use Prettier code style!" for example

[ghost]

This is output from 'similar-asserts'; in any case, I'll try to do something with this.