Add `@SuppressWarnings` to all generated classes

[semyon-levin-workato]

Hi,

Thanks for a great library!

We hit quite an unfortunate situation. We added @Deprecated to some components of our records and generated builders can't be compiled now because of the absence of @SuppressWarnings.

It can be a narrow @SuppressWarnings("deprecation"). But actually, I'd suggest adding @SuppressWarnings({"all", "cast"}) to all generated classes. Generated code is not supposed to be checked by static analysis.

PS: Adding cast to all because all doesn't include it. Take a look: projectlombok/lombok#1363

[semyon-levin-workato]

I created a PR: #274