Clean up acceptance LevelDB temp dirs

Each psf-memo-db acceptance scenario opened an isolated LevelDB directory
but close() only closed the handles, so tmp/acceptance grew without bound
(found at 961 dirs / 293 MB). Delete the scenario dir in close() and sweep
tmp/acceptance at the start of the acceptance run.

By specifier.

psf-memo-db/acceptance/acceptance.js

@@ -33,7 +33,19 @@ function ensureAps () {
     'https://github.com/unclebob/Acceptance-Pipeline-Specification.git', apsDir])
 }
 
+// Each scenario opens an isolated LevelDB directory under tmp/acceptance.
+// Remove leftovers from earlier runs (including pre-fix runs that leaked them)
+// so the directory cannot grow without bound.
+function cleanStaleWorlds () {
+  try {
+    fs.rmSync(path.join(root, 'tmp', 'acceptance'), { recursive: true, force: true })
+  } catch (err) {
+    // ignore cleanup errors
+  }
+}
+
 function main () {
+  cleanStaleWorlds()
   ensureAps()
 
   const features = fs

psf-memo-db/acceptance/lib/handlers.js

@@ -152,6 +152,13 @@ async function createWorld () {
       } catch (err) {
         // ignore close errors
       }
+      // Each scenario opens an isolated LevelDB directory. Remove it here so
+      // tmp/acceptance cannot grow without bound across runs.
+      try {
+        fs.rmSync(levelDir, { recursive: true, force: true })
+      } catch (err) {
+        // ignore cleanup errors
+      }
     }
   }
 }