fix(adjoint): update EpsType typing in DerivativInfo

[groberts-flex]

thanks @marcorudolphflex for catching this mismatch!

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Note

Low Risk
Type-alias/import change only; no runtime logic or numerical behavior is modified.

Overview
Updates DerivativeInfo permittivity typing by removing FreqDataArray usage and redefining EpsType to ScalarFieldDataArray, aligning eps_in/eps_out annotations with the actual data structures.

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[github-actions]

Diff Coverage

Diff: origin/develop...HEAD, staged and unstaged changes

• tidy3d/components/autograd/derivative_utils.py (100%)

Summary

• Total: 2 lines
• Missing: 0 lines
• Coverage: 100%