migrate-to-shoehorn

Replace `as Type` casts with fromPartial() from @total-typescript/shoehorn, which accepts partial data while keeping type checking. For intentionally wrong data written as `as unknown as Type`, use fromAny() instead.

Shoehorn lets tests pass partial data while keeping TypeScript satisfied, avoiding `as` assertions. It provides fromPartial() for partial valid data, fromAny() for intentionally wrong data, and fromExact() to force a full object.

Use fromPartial() when passing partial data that still type-checks, such as faking a large Request object with only the needed properties. Use fromAny() when passing intentionally wrong data for error testing while keeping autocomplete.

No, shoehorn is intended for test code only. It exists to replace unsafe `as` assertions in tests with type-safe partial mocks, and should never be used in production code paths.

Search test files for assertions with a grep pattern like `grep -r " as [A-Z]" --include="*.test.ts" --include="*.spec.ts"`. Then replace each match with fromPartial() or fromAny() and run a type check to verify.