Accept normalized columns in adapter manifests

[Anionix]

Fixes #495

Source review: #488 (comment)

Contract

• Keep the named AdapterColumn contract for adapter-native manifests.
• Also accept the repository's existing list[NormalizedColumn] flow without conversion.
• Preserve runtime behavior; this change is static typing plus contract coverage only.

Verification

• TDD red: test_adapter_contract_keys_are_explicit rejected the previous list[AdapterColumn]-only annotation.
• Ruff: PASS.
• Focused tests: 4 passed.
• Pyright 1.1.411: 20 files, 0 errors/warnings/information.
• Targeted specification and scope reviews: PASS.
• git diff --check: PASS.
• Lean: NO_LEAN; this is a Python static-type compatibility contract.

Exact SHA: c1081633aa8ac03d05136b931bad3bbdd40bd7f0

Primary sources:

• https://docs.python.org/3/library/typing.html#typing.TypedDict
• https://docs.python.org/3/library/typing.html#typing.NotRequired
• https://typing.python.org/en/latest/spec/typeddict.html