feat(geotiff): Separate source for header fetches and data fetches

[kylebarron]

Change list

• Split sources between "header source" and "data source". I.e. we may want chunking and caching to be applied separately to different sources.
• Vendor getTile and getBytes from upstream so that we can override the source used for tile fetches.
• Always eagerly fetch TileByteCounts and TileOffsets when opening the IFDs so that we never make tiny per-tile fetches just to find the length of the tile.

Related:

• Separate caching and chunking strategies for header and tile data? blacha/cogeotiff#1431
• Figure out good caching and chunking defaults for GeoTIFF.fromUrl #294
• Will let us implement multi-fetches (Extend deck.gl tile fetching to enable multi-tile fetches #273) outside of relying on upstream @cogeotiff/core