fix(directions): show a 996 m leg as 1.0 km, not 1000 m (#1386)

Choose route distance units after rounding so near-kilometre legs display in kilometres.

Contribution by @rudycelekli.

changelog.d/1386-route-distance-kilometre.md

@@ -0,0 +1,3 @@
+- Show a route leg of 995 m or more as 1.0 km. The route summary and step
+  cards kept meters below 1000, then rounded 996 m up to "1000 m"
+  (Rudy Celekli, @rudycelekli, #1386).

docs/CURRENT-STATE.md

@@ -4081,6 +4081,10 @@ routing it shows `Routing…`, and a router miss reads
 The layer holds continuous render only while a route is drawn (the dashes
 animate). Disable clears all state.
 
+At the metre/kilometre boundary, route distance labels use the rounded
+ten-metre value to select the unit, switching to kilometres at 995 metres;
+a 996-metre leg displays as `1.0 km` rather than `1000 m`.
+
 **Keys needed: none.** Directions works on a keyless boot, and the layer is off
 until the operator turns it on.
 

src/data/directions.test.mjs

@@ -846,6 +846,8 @@ test('route numbers follow the page language and never break from their unit', (
   t.after(() => setLocale('en'));
   assert.equal(routeDistanceText(8.4), '8\u00a0m');
   assert.equal(routeDistanceText(236), '240\u00a0m');
+  assert.equal(routeDistanceText(994), '990\u00a0m');
+  assert.equal(routeDistanceText(996), '1.0\u00a0km');
   assert.equal(routeDistanceText(1500), '1.5\u00a0km');
   assert.equal(routeDistanceText(2_345_000), '2345\u00a0km');
   assert.equal(routeDurationText(39), '39\u00a0s');

src/layers/directions/index.js

@@ -112,7 +112,8 @@ export const FLIGHT_PROGRESS_MS = 250;
 export function routeDistanceText(meters) {
   if (!Number.isFinite(meters) || meters < 0) return '';
   if (meters < 100) return formatQuantity(Math.round(meters), 'm');
-  if (meters < 1000) return formatQuantity(Math.round(meters / 10) * 10, 'm');
+  const tens = Math.round(meters / 10) * 10;
+  if (tens < 1000) return formatQuantity(tens, 'm');
   const km = meters / 1000;
   return km < 10
     ? formatQuantity(km, 'km', {