Consider making the builders infallible

[Veetaha]

Hi, thank you for the awesome crate ❤️

I'd like to propose an improvement to the vergen API. It currently uses derive_builder to generate builders for various config structs. As a replacement, I propose using the bon crate.

Motivation

The problem with the builders generated by derive_builder are the following:

• The build() methods of the builders return a Result, which usually requires the users to call unwrap() on it or somehow else get rid of the error, which is an annoyance. In contrast, bon generates fully compile-time-checked builders. Forgetting to set a field triggers a compile error with a readable error message.
• derive_builder performs no checks for unintentional overwrites, while bon validates that you don't accidentally set the same field twice at compile time.
• derive_builder doesn't generate a T::builder() method, instead, it requires the users to use TBuilder::default() to create the builder.
• bon generates more ergonomic API that allows evolving it without breaking changes by default (See the compatibility page for all the possible ways to evolve your builder API in backwards-compatible way).
• bon allows for greater flexibility by allowing you to generate a builder from a function or an associated method. It's even possible to switch between derive(Builder) and #[builder] on the method named new without breaking changes.

A comparison table between builder crates can be seen on this page

---

Would you be interested in this change? I understand that this will require a major release, so I understand if you'd like to push back on this, or postpone doing it until any other reasons for the major release arise.

In any case I can submit a PR from my side if you think it's fine to do it.