Optimize tracing

[LinqLover]

Current bottlenecks during tracing are:

• [x] TDBTrace>>#maxTimeIndex (42%) - cache?
• [x] TDBTrace>>#traceAtTime:ifAbsent: (39%) - inline binary search? don't use #associations.

Remaining potential for optimization:

• [ ] SimulationContext>>#customize: (1.7%) - hard-code relevant subset of copyFrom:
• [ ] TDBMemory>>#object:priorTo:atSlot:put: (19.4%) - avoid thisContext, anything else?
• [ ] TDBTrace>>#updateMaxTimeIndex:from: (7.5%)
• [ ] TDBTrace>>#traceAtTime:ifAbsent: (18.4%) - single index for all traces?
• [ ] TDBTrace>>#enableSimulatorDuring:: Currently, we are customizing all contexts there, which makes every forward-step in a large tree an expensive operation. Would it be fine only to customize the top context instead? Or could we at least exclude dead contexts (this would still be an optimization from O(n) to O(√n))?

Ideas for reducing space consumption:

• [ ] Use dense table memory layout for certain objects/slots (i.e., Context/pc)?
• [ ] Reduce default size of TDBTrace.children? Currently, over 90% of all trace instances do have 2 children or less:

  sizes := self cursor rootTrace withAllDescendants contents collect: [:t | t children size] as: Bag.
  sizes openAsMorph.
  (sizes count: [:size | size <= 2] ) / sizes size asFloat.