fix!: Return originally passed data as select events instead of mutated ones.

[mturoci]

@marek-mihok - can you make a code review and a thorough QA to check if everything works as expected?

Breaking change alert

• The returned event data is now the same as passed in. Prior to this PR, the data could have been mutated eg when scale='time' to timestamps.
• Slight return format change: The events are returned in a flat array instead of a nested ([[]]) array for line, area plots etc.

[mturoci]

Good point. Not related to the events though so will fix in another commit.