fix: pre_hook (sync) make request mutable

[drahnr]

Obsoletes #823

[ahl]

I'm sort of surprised that we don't have a test that validates this. What will existing users of pre_hook experience other than a type error if they've specified the type in their pre_hook closure or fn?

[drahnr]

I'm sort of surprised that we don't have a test that validates this. What will existing users of pre_hook experience other than a type error if they've specified the type in their pre_hook closure or fn?

Can you rephrase, I am not sure I understand what your concern is. Do you want an interface check for the provided TokenStream or are you concern re change in behviour for existing users that expect an &Request as argument?

[ahl]

If there is an existing user of the pre_hook interface, what will those users experience with this change? Will everything just work or will compilation fail with an error?