[core] Support floating activation time on usable items

[sruon]

I affirm:

• I understand that if I do not agree to the following points by completing the checkboxes my PR will be ignored.
• I understand I should leave resolving conversations to the LandSandBoat team so that reviewers won't miss what was said.
• I have read and understood the Contributing Guide and the Code of Conduct.
• I have tested my code and the things my code has changed since the last commit in the PR and will test after any later commits.

What does this pull request do?

Grabs the activation time from item_usable as a float since some items are legitimately 0.25/0.5 timer and are currently being set to 0.

I will publish updated values in a separate commit.

Steps to test these changes

Modified an item to be 12.5s and verified with a breakpoint.