Add tests for tier syntax

Summarize the changes

Ensure that

- [ ] New code is covered by unit and integration tests. - [ ] Related issues would be automatically closed with gitlab's closing pattern (Closes #1, #2). - [ ] Public modules are documented (check the rendered version with cargo doc --open). - [ ] (if PEST grammar is changed) EBNF grammar reflects these changes (check the result with railroad diagram generator.

Next steps

• Cherry-pick to: none
• Update sbroad submodule in picodata/picodata.
• (if EBNF grammar is changed) create a follow-up issue in picodata/docs.

Closes #768 (closed)