Validate option keys passed to #change()

[vlad-pisanov]

Summary

DateTime#change and Time#change receive nearly identical keyword arguments, with one subtle difference: DateTime#change also supports start:.

The change method silently ignores invalid/unsupported keyword arguments, which makes it error-prone to typos and makes transitioning legacy codebases from DateTime to Time difficult.

The same problem affects related classes Date and TimeWithZone.

This PR enforces that all arguments passed to change are actually supported, and updates a stale comment to include :nsec and :usec as supported arguments to DateTime#change.

[adrianna-chang-shopify]

👋 Hey @vlad-pisanov, would you mind rebasing your branch again please to address conflicts? Thanks!

[adrianna-chang-shopify]

I think we also need to require "active_support/core_ext/hash/keys.rb" in both of the calculations.rb files to make use of #assert_valid_keys

[vlad-pisanov]

@adrianna-chang-shopify done! And thanks for the require reminder 🙏