fix: Make the core feature work

[flub]

Updating the support for the core feature to compile and be compatible on the API.

Also deletes some unused fields and methods the compiler was complaining about and cargo-fmt made some changes to the edited files.

We don't particularly need the core feature, however it is the only way to use the crate without depending on default features of the chrono crate. And the chrono crate has a dependency on a vulnerable version of the time crate. Switching to the core feature for this crate allows us to avoid having the vulnerability in our dependencies.

[flub]

Thanks! Any chance of publishing a new release with this?

[al8n]

Thanks! Any chance of publishing a new release with this?

Sorry, I forgot to release it. I will do it now.