Place Config::format behind the format feature flag.

[gibbz00]

Fixes: #1021

Depends upon: #1020.

[caspermeijn]

Please make this PR independent of #1020.

My reasoning:

• The current diff is unreadable
• The other PR is in draft.

[gibbz00]

Valid points 😊

Though of doing this at first, I wanted to avoid having to fix the conflicts that would arise. Do you think that this will be merged before #1020? I wouldn't mind making this an independent PR is that's the case.

[caspermeijn]

Well, from my point of view:

• prost-build: Split Config and Module into a separate module and files #1020 is in draft and this PR is not, so prost-build: Split Config and Module into a separate module and files #1020 can't be merged first
• This PR and prost-build: Split Config and Module into a separate module and files #1020 are completely unrelated, other than the same author and potential merge conflict.
• I can't execute a good review of this PR, so it either needs to be fixed or should be opened after the other merge.

The last commit of this branch seems like an improvement, so I think it makes sense to keep the PR open. I suggest making it independent and solve the merge conflict at a later time.

[gibbz00]

Alrighty, a rebase later shouldn't be too hard anyway. I've now made this PR independent of the rest.

[caspermeijn]

Please rebase to fix the merge conflict

[gibbz00]

Rebased and fixed suggestions!

[caspermeijn]

Thank you for your contribution