qbsp: add a test case where two almost-touching faces cause qbsp to blow up

testmaps/csg_fail.map

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+// Game: Quake
+// Format: Standard
+// entity 0
+{
+"classname" "worldspawn"
+"wad" "speedbz_fin.wad"
+// brush 0
+{
+( -64 -1712 -320 ) ( -64 -1840 -320 ) ( -64 -1712 -192 ) wgrnd1_grass -0 -0 -0 1 1
+( -160 -1880 176 ) ( -160 -1880 304 ) ( -160 -2008 176 ) wgrnd1_grass -0 -0 -0 1 1
+( -64 -2000 -320 ) ( 64 -2000 -320 ) ( -64 -2000 -192 ) wgrnd1_grass -0 -0 -0 1 1
+( -64 -2048 -448 ) ( -192 -2048 -448 ) ( -64 -2048 -320 ) wgrnd1_grass 0 0 0 1 1
+( 176 -1392 176 ) ( 176 -1520 176 ) ( 160 -1376 176 ) glass2 0 0 0 1 1
+( -400 -1792 64 ) ( -384 -1792 64 ) ( -400 -1664 64 ) wgrnd1_grass 0 0 0 1 1
+}
+// brush 1
+{
+( -160 -5008 192 ) ( -159.9420166015625 -5008 85440 ) ( -159.98944091796875 -90256 192 ) wgrnd1_grass 0 0 -0 1 1
+( -121.68017578125 -1728 176 ) ( -121.6805419921875 83520 175.976806640625 ) ( -81402.4453125 23975.298828125 176.4119873046875 ) hex1_3 0 0 -0 1 1
+( -144 -2000 144 ) ( -144 -2000 112 ) ( -128 -2000 144 ) wgrnd1_grass 0 0 0 1 1
+( -96 -2048 144 ) ( -112 -2048 96 ) ( -144 -2048 96 ) wgrnd1_grass 0 0 0 1 1
+( -64 -2016 128 ) ( -64 -2016 112 ) ( -64 -2032 112 ) wgrnd1_grass 0 0 0 1 1
+( -128 -2000 256 ) ( -144 -2000 256 ) ( -144 -1872 256 ) wgrnd1_grass 0 0 0 1 1
+}
+}
+// entity 1
+{
+"classname" "info_player_start"
+"origin" "-344 -2030 309"
+"angle" "-0"
+}

testmaps/csg_fail.txt

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+Example where qbsp can't decide if two brushes are touching or not, and a wrong leaf content type gets assigned as a result (the info_player_start will be standing on an invisible solid). Happens with tyrutils 0.15 as well.