move apply_expression into ImageData class and use b{ix} for band names

[vincentsarago]

this PR does:

• add apply_expression into ImageData class to avoid code duplication (this is possible because we now have a proper ImageData object out the reader methods.)
• add b prefix for band names breaking. We should have done this from the beginning!!! (e.g if you pass expression="b1,b2" band names would have been 'b1', 'b2' while indexes=(1, 2) would have given ('1', '2')

  # before
  with COGReader("cog.tif") as cog:
      img = cog.read()
      print(cog.band_names)
      >>> ["1", "2", "3"]
  
      print(cog.info().band_metadata)
      >>> [("1", {}), ("2", {}), ("3", {})]
  
      print(cog.info().band_descriptions)
      >>> [("1", ""), ("2", ""), ("3", "")]
  
      print(list(cog.statistics()))
      >>> ["1", "2", "3"]
  
  # now
  with COGReader("cog.tif") as cog:
      img = cog.read()
      print(img.band_names)
      >>> ["b1", "b2", "b3"]
  
      print(cog.info().band_metadata)
      >>> [("b1", {}), ("b2", {}), ("b3", {})]
  
      print(cog.info().band_descriptions)
      >>> [("b1", ""), ("b2", ""), ("b3", "")]
  
      print(list(cog.statistics()))
      >>> ["b1", "b2", "b3"]
  
  with STACReader("stac.json") as stac:
      print(stac.tile(701, 102, 8, assets=("green", "red")).band_names)
      >>> ["green_b1", "red_b1"]

[vincentsarago]

unrelated to the PR goal!

[vincentsarago]

here we overwrite the bands that will be use as expression.

FYI:

• we now have band_names = ["green_b1", "red_b1"]
• up to now we are assuming that expression=green/red mean there is only one band in each dataset THIS IS BAD
• in this line we tell apply_expression to overwrite the bands_names to ["green", "red"] to keep the compatibility.
• The proper expression should be expression="green_b1/red_b1" but this will be maybe too big of a breaking change

@geospatial-jeff any advice here?

[vincentsarago]

opened #524 to talk about this

[geospatial-jeff]

The proper expression should be expression="green_b1/red_b1" but this will be maybe too big of a breaking change

I think we should do something like this. We are breaking things anyways so might as well get it right now. Representing the full hierarchy of asset::band seems like the best way to support applying expressions across multi-band assets.

[vincentsarago]

changed the file names to make it more explicit

[geospatial-jeff]

Left some thoughts in #524