Add a new `SessionConfig` object to allow advanced configuration of the `Downloader`

[Cadair]

This PR introduces breaking API changes, it will form a 2.0 release of parfive.

fixes #38 fixes #29

This PR is motivated by the fact that we have been slowly growing more and more keyword arguments, environment variables etc at various levels in the class.

This PR cleans up the environment variable handling and keyword arguments to the main Downloader class by making a config object which holds the state for the instance. As well as this some of the more obscure keyword arguments are moved into a SessionConfig object.

Changes in this PR

• A new PARFIVE_HIDE_PROGRESS environment variable will disable all progress bars.
• The file_progress=, use_aiofiles= and notebook= keyword arguments have been moved into the new SessionConfig object which can be passed to Downloader() as the config= keyword argument.
• The headers= keyword argument to Downloader() is now deprecated in favour of passing them as part of the SessionConfig object. They will be removed in a future release.
• All environment variables are now evaluated at the time the Downloader class is instantiated (by the new config classes).
• The value of the boolean environment variables now matter, they should cast to True.
• The timeouts keyword argument has been removed from the run_download() and download() methods and replaced by an option in SessionConfig.
• It is now possible to configure the options passed to aiohttp.ClientSession with the aiohttp_session_kwargs= keyword argument to SessionConfig.
• It is now possible to configure debug or other levels of logging with SessionConifg where previously it could only be configured with an environment variable.
• It is now possible to configure the HTTP chunksize with SessionConfig and the default when not using aiofiles has been increased from 100 bytes to 1024 bytes.
• It is now possible to configure the HTTP(S) proxy URLs with SessionConfig as well as the HTTP[S]_PROXY environment variables.
• It is now possible to customise all the timeouts supported by aiohttp by passing an aiohttp.ClientTimeout object to SessionConfig.

[codecov[bot]]

Codecov Report

Merging #92 (106d5c2) into main (c52cbe3) will increase coverage by 0.84%. The diff coverage is 97.81%.

@@            Coverage Diff             @@
##             main      #92      +/-   ##
==========================================
+ Coverage   92.48%   93.33%   +0.84%     
==========================================
  Files           4        5       +1     
  Lines         466      540      +74     
==========================================
+ Hits          431      504      +73     
- Misses         35       36       +1     

Impacted Files	Coverage Δ
parfive/downloader.py	93.26% <95.34%> (-0.41%)	:arrow_down:
parfive/config.py	98.87% <98.87%> (ø)
parfive/utils.py	94.54% <100.00%> (+0.15%)	:arrow_up:

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[Cadair]

I am going to ping people who have contributed to see if anyone wants to comment on this PR, and give people a chance to ask for tweaks before I push a major release.

@GitHK @rlaker @nabobalis @dstansby

[Cadair]

Thanks for the review @GitHK, are you using the use_aiofiles= kwarg to Downloader? Would removing it cause you trouble?

[GitHK]

Thanks for the review @GitHK, are you using the use_aiofiles= kwarg to Downloader? Would removing it cause you trouble?

No issue for me. Go ahead and remove it. We usually do periodic updates and fix these small issues. It helps a lot when libraries point breaking changes in the changelog, upgrades are much smoother.

[Cadair]

@GitHK Thanks! I have pulled it now, I am going to keep headers around for people using previous versions of sunpy.

[Cadair]

I have pushed 2.0.0rc1 up to PyPI if people want to test this and open any issues.

[nabobalis]

Overall:

👍 on pydantic, such a great library. 👍 on the config refactor, makes things much clearer in the main downloader code. 👎 on adding type hints and using black.