[LUA] Add Ruszor family mixin and mob files

[ampitere]

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?

Adds Ruszor family mixin and mob files. To be used in: #5731

Steps to test these changes

Nothing really to test yet but you could add Stoneskin status and set their animation sub to something other than 0.

1. !zone Beaucedine Glacier [S]
2. !mobhere 17334289