### Description

Follow-up of #98360: when there is a single filter, the collector could save the overhead of the priority queue (both in `collect()` and `competitiveIterator()`), which would likely result in a speedup.
server/src/main/java/org/elasticsearch/search/aggregations/bucket/filter/FiltersAggregator.java
if (obj == null) {
                return false;
            }
            if (getClass() != obj.getClass()) {
                return false;
            }
            KeyedFilter other = (KeyedFilter) obj;
            return Objects.equals(key, other.key) && Objects.equals(filter, other.filter);
        }
    }
    /**
     * Build an {@link Aggregator} for a {@code filters} aggregation. If there
     * isn't a parent, there aren't children, and we don't collect "other"
     * buckets then this will a faster {@link FilterByFilterAggregator} aggregator.
     * Otherwise it'll fall back to a slower aggregator that is
     * {@link Compatible} with parent, children, and "other" buckets.
     */
    public static FiltersAggregator build(
        String name,
        AggregatorFactories factories,
        List<QueryToFilterAdapter> filters,
        boolean keyed,
        String otherBucketKey,
        boolean keyedBucket,
        AggregationContext context,
        Aggregator parent,
        CardinalityUpperBound cardinality,
        Map<String, Object> metadata
    ) throws IOException {
        FilterByFilterAggregator.AdapterBuilder<FilterByFilterAggregator> filterByFilterBuilder =