TypeScript guidelines: Document any requirement for callback parameters subject to bidirectional assignment

[MajorLift]

I keep encountering this pattern. Seems worth documenting, especially given function contravariance is confusing enough on its own.

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Note

Low Risk
Documentation-only change that clarifies a narrow TypeScript typing edge case; no runtime or behavior impact.

Overview
Adds a new TypeScript guideline section explaining when any is the only workable type for callback parameter positions that are constrained from both sides (bidirectional assignment under --strictFunctionTypes contravariance).

Includes a concrete example contrasting unknown, never, and any, plus guidance that the eslint-disable is intentional and scoped to avoid propagating any.

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