refactor(router): use definite assignment assertions in createDeferred

[syedsohailhussain1]

Refactors createDeferred to use definite assignment assertions (!) for resolve and reject, completely eliminating the need for @ts-ignore comments.
Because the Promise executor runs synchronously, resolve and reject are guaranteed to be assigned before they are returned. Using ! explicitly communicates this guarantee to the TypeScript compiler in a type-safe way.

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