feat: Adding settings, utils, write to S3, and writer close

[malteos]

This PR integrates a couple of general changes from the EOT PR (#54):

• Settings variables are loaded from environment variables in settings.py
• Common CLI methods are moved to utils.py
• Read and write to S3 (via fsspec).
• Missing writer.close() statement is added to CLI and example.

[codecov]

Codecov Report

❌ Patch coverage is 96.66667% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.05%. Comparing base (b6f5f02) to head (b9f01d4).

Files with missing lines	Patch %	Lines
cdx_toolkit/cli.py	75.00%	1 Missing ⚠️
cdx_toolkit/commoncrawl.py	80.00%	1 Missing ⚠️
cdx_toolkit/utils.py	97.22%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #67      +/-   ##
==========================================
+ Coverage   95.78%   97.05%   +1.27%     
==========================================
  Files           7        9       +2     
  Lines         877      918      +41     
==========================================
+ Hits          840      891      +51     
+ Misses         37       27      -10     

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[malteos]

Given that the test coverage check fails on this one, what about adjusting the coverage check to a fixed value instead of the last coverage value?

[wumpus]

While the coverage check failed, I don't think it will cause a problem in the next CI run? It's just a slightly easier hurdle next time.

[malteos]

While the coverage check failed, I don't think it will cause a problem in the next CI run? It's just a slightly easier hurdle next time.

I added additional unit tests which should increase the coverage above the threshold.

However, codecov seemed to stopped working after moving the repo to the CC org. I already requested access to the org. I guess you just need to approved codecov again @wumpus.