Improve RollingWindow.GetEnumerator performance

[starteleport]

Rationale

The RollingWindow.GetEnumerator method allocates a new list for each invocation and copies values to the list via this[int], which in turn enters/exits reader lock for each invocation. I was able to speed up this method by more than 50% in terms of execution time and achieve marginally better memory consumption by switching from List<T> to T[] and inlining the respective part of this[int].

Many built-in indicators as well as some reasonable real-world use cases for RollingWindow would benefit from this change in backtesting/optimisation.

Potential Solution

#8444

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