Turn on faster place delay matrix loader by default

[vaughnbetz]

@amin1377 has created a place delay matrix loader that uses the router lookahead to populate it. Since the router lookahead uses a Djikstra flood algorithm (all dests path search) it is faster than many (dx,dy) routings, which is what the placer currently uses to load the place delay matrix.

Proposed Behaviour

We should change to building the place delay matrix from the router lookahead, for speed.

Current Behaviour

Slower profiling of the architecture using repeated invocations of the router for different dx,dy

Possible Solution

Make the new method the default, after gathering QoR data on vtr, titan and koios to show that works well. Test on both 2D and 3D architectures.

Context

place delay matrix calculation can get slow (600 s for a big circuit) and slows more for 3D architectures (can be 24 hours for a big design).