geotiff: Set larger initial read size

https://github.com/blacha/cogeotiff/blob/8f16769e4f485510916e6807e2a2e2a5da9f70cf/packages/core/src/tiff.ts#L16-L20

Not sure how you set this. Apparently like this?

```ts
Tiff.DefaultReadSize = 64 * 1024;
```