Resampler::push previously closed the open bar and opened a new one for
any candle whose bucket differed from the open bar, including buckets
strictly before it — silently corrupting the output for out-of-order
input. TickAggregator::push already rejects this case with an error.
Change push to return Result<Option<Candle>>: candles in an earlier
bucket than the open bar now yield Error::Malformed, matching the
aggregator. resample_all propagates the error via `?`. The doc comment
keeps the input/output multiple relationship as a documented caller
responsibility, since Resampler does not know the input timeframe.
kingchenc
80295eec87