clippy suggestions and warning removal

[clux]

fixes:

1. unused imports for docs (made explicit, or removed when unused afaikt)
2. unused imports + attr style
3. clone_from rather than assigning clone
4. chrono's duration's now needs unwrap which is not const - Ergonomic replacements for panicking APIs. chronotope/chrono#1491

To see what the warnings looked like an hour ago. Look at the files annotated in the previous PR: https://github.com/kube-rs/kube/pull/1435/files#file-kube-client-src-client-mod-rs-L10

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 72.2%. Comparing base (959986a) to head (f49d4ed).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #1436   +/-   ##
=====================================
  Coverage   72.2%   72.2%           
=====================================
  Files         78      78           
  Lines       6546    6546           
=====================================
  Hits        4722    4722           
  Misses      1824    1824           

Files	Coverage Δ
kube-client/src/api/entry.rs	80.3% <100.0%> (ø)
kube-client/src/client/auth/oidc.rs	57.3% <100.0%> (ø)
kube-client/src/client/mod.rs	72.2% <ø> (ø)
kube-client/src/lib.rs	75.2% <ø> (ø)
kube-runtime/src/events.rs	97.3% <ø> (ø)
kube-runtime/src/reflector/object_ref.rs	69.4% <ø> (ø)
kube/src/mock_tests.rs	97.9% <ø> (ø)
kube-client/src/client/auth/mod.rs	50.5% <83.4%> (ø)