`useSWRImmutable` ignores hook-level `refreshInterval` since 2.4.0 (regression of #4208)

Bug report

Description / Observed Behavior

Since v2.4.0, useSWRImmutable ignores a refreshInterval passed directly to the hook, not just one inherited from a global <SWRConfig>.

#4208 ("fix: Ensure useSWRImmutable overrides global refreshInterval") added this line to the immutable middleware:

config.refreshInterval = 0

However, middleware runs after the hook-level options have been merged with the context config.

At that point the middleware cannot distinguish a globally configured refreshInterval from one passed as hook options, so it silently disables both. Polling that worked on ≤ 2.3.x stops with no error or warning after upgrading.

Expected Behavior

A refreshInterval passed directly to useSWRImmutable(key, fetcher, { refreshInterval }) should still be honored — only a refreshInterval inherited from a parent <SWRConfig> (the case #4208 was about) should be ignored.

If ignoring the hook-level option is intentional, it would be worth documenting as a breaking change, since it silently changes runtime behavior in a minor release.

Repro Steps / Code Example

import useSWRImmutable from 'swr/immutable'

function Status() {
  // On swr 2.3.6: fetches every second.
  // On swr >= 2.4.0: fetches exactly once, refreshInterval is discarded.
  const { data } = useSWRImmutable('/api/status', fetcher, {
    refreshInterval: 1000,
  })

  return <span>{data?.status}</span>
}

No global <SWRConfig> is involved.

https://codesandbox.io/p/sandbox/thqfwl

Additional Context

SWR version: 2.5.0 (regression introduced in 2.4.0 via #4208; 2.3.6 behaves as expected).