fix(traffic): give paired TomTom sides of one street a two-way share of dots

TomTom draws a two-way street whose directions differ as two one_side
lines on one centreline, and each got a one-way road's full share of
simulated vehicles, so the street drew twice the dots of the same street as
one full-coverage line or a two-way OSM road. A one_side line with an
opposite-direction one_side line within 5 m of at least two of three points
along it now gets a two-way direction's half share. On the decoded Austin
flow fixture every one_side line is paired, and road length weighted by
direction share falls from 553 to 417 km. Pairing a 16-tile area takes
about 41 ms per road pass. Refs #1455.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/CURRENT-STATE.md

@@ -5897,6 +5897,11 @@ easier to meet (detection is now on more often), but does not create it.
   TomTom draws only flow-tile lines with their own flow; roads without flow
   are not drawn and the status says so. A `full`-coverage flow line carries
   both travel directions, a `one_side` line the direction it is drawn in.
+  When an opposite-direction `one_side` line runs within 5 m of at least two
+  of three points a quarter, half and three quarters along a `one_side` line,
+  the two are one street's directions and each
+  gets a two-way direction's half share of dots, so the street is as dense as
+  one `full` line (#1455).
   OSM draws OpenFreeMap roads with flow matched onto them (below). Hybrid
   draws eligible TomTom motor-road lines and adds OpenFreeMap roads only where no eligible TomTom line
   runs within 35 m in the same travel direction (30 degrees), tested every