Validate Super-Tuning index persistence across adapters

[DaoyuanLi2816]

Summary

• reject adding Super-Tuning adapters with conflicting save_precomputed_indices values, because index persistence is shared by the model's buffer dictionary
• keep multiple adapters with one consistent persistence setting supported
• cover both persistence values and both mixed insertion orders with regression tests

Closes #3660.

Coordination

Approved by @BenjaminBossan in #3660 (comment).

Tests

• Before the fix, the two mixed-value regression cases failed while the three consistent cases passed.
• pytest tests/test_initialization.py -k TestSupertuningInitialization -q --no-cov --regression (5 passed)
• pytest tests/ -k supertuning -q --no-cov --regression (697 passed, 227 skipped, 35476 deselected)
• Ruff 0.16.4 check and format check passed
• git diff --check passed

AI assistance

I used Codex to help investigate, draft, and test this change. I reviewed every changed line, understand and can defend the change, and ran the tests listed above.