PNS router: Tracks are not on the grid

Description

• When dragging routes, they should end up at a sane position
• With 0.5mm wide tracks and 0.25mm wide clearance, the tracks that get dragged as close as possible to each other should also be on the 0.25mm grid.
• I would expect the 70.74952mm value to be 70.75mm instead.
• The following demo shows that this is not true

Steps to reproduce

• Create new Project
• Add two 1x8 connectors with 2.0mm pitch footprint, place them on the grid
• Set DRC values (track-track-dist 0.25mm, min-track-width 0.5mm)
• route straight connections
• observe that all routes are on the grid
• drag the routes around, so they are at the minimal distance

KiCad Version

Application: KiCad PCB Editor

Version: (6.0.1), release build

Libraries:
	wxWidgets 3.0.5
	libcurl/7.74.0 OpenSSL/1.1.1k zlib/1.2.11 brotli/1.0.9 libidn2/2.3.0 libpsl/0.21.0 (+libidn2/2.3.0) libssh2/1.9.0 nghttp2/1.43.0 librtmp/2.3

Platform: Linux 5.10.0-10-amd64 x86_64, 64 bit, Little endian, wxGTK, i3, x11

Build Info:
	Date: Jan  7 2022 23:17:47
	wxWidgets: 3.0.5 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
	Boost: 1.74.0
	OCC: 7.5.1
	Curl: 7.74.0
	ngspice: 34
	Compiler: GCC 10.2.1 with C++ ABI 1014

Build settings:
	KICAD_USE_OCC=ON
	KICAD_SPICE=ON