Follow-up: Align top/bottom surface generation with Orca/SuperSlicer

[max-scopp]

Short follow-up to improve our top/bottom surface implementation parity with established slicers.

• switch solid surface spacing to nozzle-based width
• alternate surface infill angle per layer
• add surface inset/overlap handling vs perimeters
• fix disconnected contour chaining fallback
• tighten contour matching precision
• add bridge-oriented bottom surface path

References:

• PR: Add configurable top/bottom surface generation with rectilinear infill #34
• Orca LayerRegion: https://github.com/SoftFever/OrcaSlicer/blob/main/src/libslic3r/LayerRegion.cpp
• Orca FillRectilinear: https://github.com/SoftFever/OrcaSlicer/blob/main/src/libslic3r/Fill/FillRectilinear.cpp
• Orca Surface types: https://github.com/SoftFever/OrcaSlicer/blob/main/src/libslic3r/Surface.hpp
• SuperSlicer LayerRegion: https://github.com/supermerill/SuperSlicer/blob/master/src/libslic3r/LayerRegion.cpp
• SuperSlicer Surface types: https://github.com/supermerill/SuperSlicer/blob/master/src/libslic3r/Surface.hpp