Propagate client's adapter to API categories

[WilkenSteiner]

Propagate the adapter used by the client to all handlers registered on the client.

Previously, setting the adapter (and thus session/connection pool) on the client after initialization would only replace the adapter owned by the client, leaving the adapters of all API categories untouched.

Notes

• If the current behaviour was by design, I will extend the docstrings instead. The new behaviour seems more intuitive to me, also more in line with other methods (e.g. the URL setter on the client).
• Added a regression test.

[briantist]

Hi @WilkenSteiner ! Thanks for this submission, I will have to take some time to go over it in a little more detail.

While the original designers are not active here anymore, off the top of my head, I would say that it was probably expected that the adapter would not b re-assigned after Client instantiation, though the fact that the .adapter setter was defined would make that confusing.

So I am inclined to agree that this is more intuitive, but let me think about it a bit and discuss with the other maintainers.

Also huge thanks for adding a regression test!

[briantist]

@WilkenSteiner by the way, I've just created a poll and discussion topic about the Adapter system, and I'd appreciate a vote and/or some feedback if you have a few moments:

• Help determine the future of `hvac`'s Adapter system #940

[WilkenSteiner]

@briantist Thank you for considering and putting a more structural spin on it! I left a comment in the poll with my use case.

[briantist]

@WilkenSteiner would you rebase this? The CI should be fixed now I was able to rebase for you

[codecov]

Codecov Report

Merging #939 (477ebb5) into develop (026d6b5) will increase coverage by 0.30%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop     #939      +/-   ##
===========================================
+ Coverage    81.34%   81.64%   +0.30%     
===========================================
  Files           65       65              
  Lines         2969     3002      +33     
===========================================
+ Hits          2415     2451      +36     
+ Misses         554      551       -3     

Impacted Files	Coverage Δ
hvac/api/system_backend/__init__.py	100.00% <ø> (+3.84%)	⬆️
hvac/v1/__init__.py	87.26% <100.00%> (+3.43%)	⬆️
hvac/api/auth_methods/mfa.py	100.00% <0.00%> (ø)
hvac/api/secrets_engines/kv.py	100.00% <0.00%> (ø)
hvac/api/secrets_engines/identity.py	94.00% <0.00%> (+0.02%)	⬆️
hvac/utils.py	77.27% <0.00%> (+0.20%)	⬆️
hvac/adapters.py	86.73% <0.00%> (+0.27%)	⬆️
hvac/api/vault_api_category.py	95.12% <0.00%> (+0.67%)	⬆️