MultiSearch with Union=true does not unmarshal returned hits field

[TobiasPressler]

Issue Description

When using the MultiSearch method with Union: true, the TypeSense server returns search results in a field named hits in the response. However, the Go client appears to only look for a field named results, causing the response data to be inaccessible.

Steps to Reproduce

// Create boolean, string and integer values for parameters
unionTrue := true
queryString := "search term"
pageNum := 1
resultsPerPage := 20

multiSearchResp, err := client.MultiSearch(ctx, &api.MultiSearchParams{
    Page:    &pageNum,
    PerPage: &resultsPerPage,
}, api.MultiSearchSearchesParameter{
    Union: &unionTrue,
    Searches: []api.MultiSearchCollectionParameters{
        {
            QueryBy:    &queryString,
            Q:          &queryString,
            Collection: &[]string{"collection-1"}[0],
        },
        {
            QueryBy:    &queryString,
            Q:          &queryString,
            Collection: &[]string{"collection-2"}[0],
        },
    },
})

Expected Behavior

The multiSearchResp should contain the search results accessible via a structured property.

Actual Behavior

The response contains the data in a field named hits, but the client doesn't properly map this field, making the search results inaccessible through the API.