Use compile-time checked infallible builders

[Veetaha]

Closes #372. The diff is big because basically all tests use builders, so I had to do a lot of boilerplate changes to the builder syntax. Examples of changes:

GitBuilder::deault().build()?;
// vvv
Git::builder().build();

I also changed the all_*() methods to be part of the type itself instead of the builder struct, because they just return the type itself directly, and now that builders are ment to be created with T::builder() it's easier to call T::all_* when T is already imported into scope.

GitBuilder::all_git();
// vvv
Git::all_git();

Also builders moved from by-reference to by-value self, because bon generates a type-state-based builder that changes its type on every setter call.

For some methods like TBuilder::all(&mut Self) I had to do a change all(self) -> Self) and that this method can be only called at the beginning of the builder method call chain. For example T::builder().all().foo().build() works, while this doesn't compile: T::builder().foo().all().build(), because .all() is only available at the start.