[Flight] Clear chunk reason after successful module initialization (#36024)

When `requireModule` triggers a reentrant `readChunk` on the same module
chunk, the reentrant call can fail and set `chunk.reason` to an error.
After the outer `requireModule` succeeds, the chunk transitions to
initialized but retains the stale error as `reason`.

When the Flight response stream later closes, it iterates all chunks and
expects `reason` on initialized chunks to be a `FlightStreamController`.
Since the stale `reason` is an `Error` object instead, calling
`chunk.reason.error()` crashes with `TypeError: chunk.reason.error is
not a function`.

The reentrancy can occur when module evaluation synchronously triggers
`readChunk` on the same chunk — for example, when code called during
evaluation tries to resolve the client reference for the module that is
currently being initialized. In Fizz SSR, `captureOwnerStack()` can
trigger this because it constructs component stacks that resolve lazy
client references via `readChunk`. The reentrant `requireModule` call
returns the module's namespace object, but since the module is still
being evaluated, accessing the export binding throws a TDZ (Temporal
Dead Zone) `ReferenceError`. This sets the chunk to the errored state,
and the `ReferenceError` becomes the stale `chunk.reason` after the
outer call succeeds.

This scenario is triggered in Next.js when a client module calls an
instrumented API like `Math.random()` in module scope, which
synchronously invokes `captureOwnerStack()`.