Clean-up/Refactoring of old code

[bigcat88]

Because initially the project was written for a different AppAPI authentication, where all transmitted data was signed - there was a lot of unnecessary code left.

This pull request will cover it all, total refactoring and simplification of the code.

After this, it will be possible to make public methods for communicating with Nextcloud, which would make it easier to connect third-party packages.

It is also necessary to clean up the code before adding asynchronous methods.

Changes proposed in this pull request:

• set AUTHORIZATION-APP-API header with help of event_hook
• set default timeout during httpx.adapter creation
• set base_url during httpx.adapter creation
• download_directory_as_zip: directly call session.adapter.stream (removed _session.get_stream)
• all DAV methods now directly call _session.adapter_dav.XXX (removed _session.dav / _session.dav_stream)
• removed _session.request and _sessions.request_json - instead directly call session.adapter
• response_headers are now set with help of httpx.event_hooks
• other internal code refactoring

[codecov]

Codecov Report

Merging #177 (418f7c1) into main (695b5a5) will increase coverage by 0.02%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #177      +/-   ##
==========================================
+ Coverage   99.81%   99.84%   +0.02%     
==========================================
  Files          36       36              
  Lines        3330     3277      -53     
==========================================
- Hits         3324     3272      -52     
+ Misses          6        5       -1     

Files	Coverage Δ
nc_py_api/_exceptions.py	100.00% <100.00%> (ø)
nc_py_api/_preferences.py	100.00% <100.00%> (ø)
nc_py_api/_preferences_ex.py	100.00% <100.00%> (ø)
nc_py_api/_session.py	99.13% <100.00%> (+0.15%)	⬆️
nc_py_api/_talk_api.py	100.00% <100.00%> (ø)
nc_py_api/activity.py	100.00% <100.00%> (ø)
nc_py_api/apps.py	100.00% <100.00%> (ø)
nc_py_api/calendar.py	100.00% <100.00%> (ø)
nc_py_api/ex_app/ui/files_actions.py	100.00% <100.00%> (ø)
nc_py_api/ex_app/ui/resources.py	100.00% <100.00%> (ø)
... and 10 more