feat(crdv2): implement node change notification mechanism

[l1b0k]

• Add Notifier and Subscription interfaces for node change notifications
• Integrate notifications with CRDV2 to improve IP allocation efficiency
• Refactor IP allocation logic to use the new notification system
• Optimize performance by reducing unnecessary API calls and improving concurrency

[codecov]

Codecov Report

❌ Patch coverage is 74.86911% with 48 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.74%. Comparing base (ff107f0) to head (c6538a9).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/eni/crdv2.go	68.29%	26 Missing and 13 partials ⚠️
pkg/eni/notify.go	86.76%	7 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #872      +/-   ##
==========================================
+ Coverage   44.55%   45.74%   +1.18%     
==========================================
  Files         130      131       +1     
  Lines       18988    19087      +99     
==========================================
+ Hits         8460     8731     +271     
+ Misses       9634     9442     -192     
- Partials      894      914      +20     

Flag	Coverage Δ
unittests	45.74% <74.86%> (+1.18%)	⬆️

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