Memory allocation issue

Nobody has claimed this yet.

Here's a tile-reduce process that's run for the planet. I'm expecting the script to release memory after processing a tile. Instead process keeps taking up more memory space without freeing up memory for the processed tiles and fails at a point due to memory allocation issue.

Time Spent| Memory
-----------|---------
Before beginning the process|
10s|
30s|
After 1 minute|

### Map script

```
'use strict';
module.exports = function(tileLayers, tile, writeData, done) {
done();
};
```

### Reduce script

```
'use strict';

var tileReduce = require('@mapbox/tile-reduce');
tileReduce({
zoom: 12,
map: path.join(__dirname, 'index.js'),
sources: [{
name: 'osm',
mbtiles: 'latest.planet.mbtiles',
}

]
})
```

I'd need help to resolve this issue.

Start by reproducing the tile-reduce run using the shown map script, reduce script, and latest.planet.mbtiles source, then inspect memory growth across tiles. Read the @mapbox/tile-reduce entry points involved in map and reduce processing and determine whether memory is retained after done() completes. Done means identifying a reproducible cause and confirming that memory no longer grows until allocation fails.

Written by the indexing model from the issue text.