Replace EarthAccessFile with classes inheriting from specific AbstractBufferedFile subclasses

[itcarroll]

Fixes #610

This PR provides an "explicit is better than implicit" solution to fixing the method resolution order (MRO) on the (now former) EarthAccessFile (#610). The bug was that EarthAccessFile tried to proxy both s3fs.S3File and fsspec.implmentations.http.HTTPFile, but failed to proxy those methods also defined on the superclass fsspec.spec.AbstractBufferedFile from which all three inherited. My first attempted fix (PR #620) removed fsspec.spec.AbstractBufferedFile from the MRO of EarthAccessFile. While this did proxy methods correctly, usage was broadly broken because each EarthAccessFile was no longer an instance of the file-like object proxied (which was important, in particular for xarray.open_dataset!).

Why proxy at all? The file-like objects that earthaccess.open provides must be pickleable AND the un-pickling process needs to be able to change the particular type of file-like object used, an essential part of the hand-off of file-like objects between xarray running locally and dask workers in the cloud.

What this PR does:

• replaces class EarthAccessFile(fsspec.spec.AbstractBufferedFile) with a suite of (currently three) classes that could be returned by fs.open where fs is either an S3FileSystem or an HTTPFileSystem.
  • EarthaccessS3File(EarthaccessMixin, S3File)
  • EarthaccessHTTPFile(EarthaccessMixin, HTTPFile)
  • EarthaccessHTTPStreamFile(EarthaccessMixin, HTTPStreamFile)
• adds the EarthaccessMixin to implement the __reduce__ method for custom pickling
• replace the logic of the __reduce__ callable, the make_instance function, to avoid "double pickling" (no more dumps)

NOTE: Because #620 was merged, the "Files changed" in this PR are misleading relative to the original implementation. The best commit to reference for comparison is from right before the merge.

Still in progress:

• documentation (both user documentation and code comments)
• the new tests need to be integration tests rather than unit tests (i think) to use earthdata authentication

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Please do your best to complete these requirements! If you need help with any of these
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📚 Documentation preview 📚: https://earthaccess--828.org.readthedocs.build/en/828/