### 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
}
        /**
         * Read from a stream.
         */
        public KeyedFilter(StreamInput in) throws IOException {
            key = in.readString();
            filter = in.readNamedWriteable(QueryBuilder.class);
        }
        @Override
        public void writeTo(StreamOutput out) throws IOException {
            out.writeString(key);
            out.writeNamedWriteable(filter);
        }
        public String key() {
            return key;
        }
        public QueryBuilder filter() {
            return filter;
        }
        @Override
        public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
            builder.field(key, filter);
            return builder;
        }
        @Override
        public int hashCode() {
            return Objects.hash(key, filter);
        }
        @Override
        public boolean equals(Object obj) {