Streaming Mean and Mode Class

AkunaCapital receives a stream of integer observations from a market-data feed. Implement process_operations(operations) to insert observations and answer statistical queries without recomputing over all prior values.

Each operation is one of:

1. ["insert", x], add integer x to the stream.
2. ["mean"], return the arithmetic mean as a float.
3. ["median"], return the median. For an even number of observations, return the average of the two middle values.
4. ["mode"], return the value with the highest frequency. If several values tie, return the smallest value.
5. ["stats"], return an object containing mean, median, and mode.

Return a list containing one result for every query operation, in order. Insert operations produce no result. All query operations occur after at least one insertion.