Refactor infra controller, add kubevirt NetworkManager

[stoyanr]

How to categorize this PR?

/area quality /kind technical-debh /priority normal /platform kubevirt

What this PR does / why we need it: Refactors the infra controller to follow the model of the worker controller:

• Extract NAD management logic into kubevirt.NetworkManager
• Refactor kubevirt.DataVolumeManager for consistency with kubevirt.NetworkManager: remove unused methods, add logging and retry on conflict, update method signatures, etc.
• Introduce client caching for both managers
• Ensure that loggers are always injected and used consistently in all controllers

Which issue(s) this PR fixes: Fixes #

Special notes for your reviewer: Based on #83 , which should be merged first before merging this one.

Release note:

NONE

[gardener-robot]

@stoyanr Label kind/technical-debh does not exist.

[stoyanr]

/cc @mfranczy