chore: deprecate levelZero and levelOne

[kim-em]

This PR deprecates levelZero in favor of Level.zero and levelOne in favor of the new Level.one, and updates all usages throughout the codebase. The levelZero alias was previously required for computed field data to work, but this is no longer needed.

🤖 Prepared with Claude Code

[mathlib-lean-pr-testing]

Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 738688efeed68cd70c7ae8a51e07d63e0095b73e --onto 87ec768a509c45987a7d73258da0cc1ef047925c. You can force Mathlib CI using the force-mathlib-ci label. (2026-02-27 02:45:21)

[leanprover-bot]

Reference manual CI status:

• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase 738688efeed68cd70c7ae8a51e07d63e0095b73e --onto 8038a8b8904f89ad9542c8eda11379f8f006eab1. You can force reference manual CI using the force-manual-ci label. (2026-02-27 02:45:22)