Optimizations to the native GeoTiff reader.

This takes the geotiff reading time down for `aspect.tif` from over a second to under 100 ms. 
#### Before
```
[info] [gdal] Run 0 took 45 ms.
[info] [gdal] Run 1 took 38 ms.
[info] [gdal] Run 2 took 37 ms.
[info] [gdal] Run 3 took 38 ms.
[info] [gdal] Run 4 took 51 ms.
[info] [native] Run 0 took 1454 ms.
[info] [native] Run 1 took 1847 ms.
[info] [native] Run 2 took 1338 ms.
[info] [native] Run 3 took 1308 ms.
[info] [native] Run 4 took 1258 ms.
[info] NoData value is -9999.0, converting to NaN
[info] NoData value is -9999.0, converting to NaN
[info] [geotools] Run 0 took 531 ms.
[info] NoData value is -9999.0, converting to NaN
[info] [geotools] Run 1 took 415 ms.
[info] NoData value is -9999.0, converting to NaN
[info] [geotools] Run 2 took 423 ms.
[info] NoData value is -9999.0, converting to NaN
[info] [geotools] Run 3 took 286 ms.
[info] NoData value is -9999.0, converting to NaN
[info] [geotools] Run 4 took 284 ms.
```
[info] **GDAL took 41 ms.**
[info] **GeoTools took 387 ms.**
[info] **Native reader took 1441 ms.**

#### After
```console
[info] [gdal] Run 0 took 53 ms.
[info] [gdal] Run 1 took 45 ms.
[info] [gdal] Run 2 took 43 ms.
[info] [gdal] Run 3 took 43 ms.
[info] [gdal] Run 4 took 56 ms.
[info] [native] Run 0 took 86 ms.
[info] [native] Run 1 took 89 ms.
[info] [native] Run 2 took 62 ms.
[info] [native] Run 3 took 75 ms.
[info] [native] Run 4 took 61 ms.
[info] NoData value is -9999.0, converting to NaN
[info] NoData value is -9999.0, converting to NaN
[info] [geotools] Run 0 took 616 ms.
[info] NoData value is -9999.0, converting to NaN
[info] [geotools] Run 1 took 420 ms.
[info] NoData value is -9999.0, converting to NaN
[info] [geotools] Run 2 took 440 ms.
[info] NoData value is -9999.0, converting to NaN
[info] [geotools] Run 3 took 294 ms.
[info] NoData value is -9999.0, converting to NaN
[info] [geotools] Run 4 took 287 ms.
```
[info] **GDAL took 48 ms.**
[info] **GeoTools took 411 ms.**
[info] **Native reader took 74 ms.**