Fix return types for pagination handlers

[SeppahBaws]

This fixes a subtle bug that crept in with #1352, where the return types for loadNextPage and loadPreviousPage became Promise<QueryResult<_Data, _Input> | undefined> instead of the Promise<QueryResult<_Data, _Input>> as defined by the CursorHandlers type.

To help everyone out, please make sure your PR does the following:

• [ ] Update the first line to point to the ticket that this PR fixes
• [ ] Add a message that clearly describes the fix
• [ ] If applicable, add a test that would fail without this fix
• [ ] Make sure the unit and integration tests pass locally with pnpm run tests and cd integration && pnpm run tests
• [ ] Includes a changeset if your fix affects the user with pnpm changeset

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🦋 Changeset detected

Latest commit: 08cdc95aaa8ddc8555024ae33bc34b8924c225c6

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 9 packages

| Name | Type | | ----------------------------------- | ----- | | houdini-svelte | Patch | | houdini-plugin-svelte-global-stores | Patch | | houdini-adapter-auto | Patch | | houdini-adapter-cloudflare | Patch | | houdini-adapter-node | Patch | | houdini-adapter-static | Patch | | houdini-react | Patch | | houdini | Patch | | create-houdini | Patch |

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