expand oparator have wrong typing

Describe the bug

Expand operator have wrong typings of project function. From the description it applies the projection function to every source value as well as every output value, so the project function should receive both – input and output types.
But actually the types are implemented like this

export function expand<T, O extends ObservableInput<unknown>>(
  project: (value: T, index: number) => O,
  concurrent = Infinity,
  scheduler?: SchedulerLike
): OperatorFunction<T, ObservedValueOf<O>>

That means i can return another type from the project function and will not receive a compilation error.

Expected behavior

The type should be like this

export function expand<T, O extends ObservableInput<unknown>>(
  project: (value: T | ObservedValueOf<O>, index: number) => O,
  concurrent = Infinity,
  scheduler?: SchedulerLike
): OperatorFunction<T, ObservedValueOf<O>>

Reproduction code

No response

Reproduction URL

No response

Version

7.6.0

Environment

No response

Additional context

No response

Start at the TypeScript declaration for the expand operator and compare its project callback type with the expected signature in the issue. Trace the operator's existing type coverage, then verify that a project function receiving both source and output value types is accepted while incompatible return types are rejected.