Include `setNativeToken`

[smol-ninja]

Context: https://github.com/sablier-labs/company-discussions/discussions/115#discussioncomment-12504570

[smol-ninja]

Same question as #13 (comment).

Given we now have the code for collect-fee, it will be easy to include it as well now. But the question is since default fee can only be set by the admin, how would we do it without exposing the admin's private key or more complicated if its a multisig.

And if we only need the calldata for the tx, we can use cast sig from Foundry CLI.