fix: skip the reconcile when spec does not change

[zhiying-lin]

What type of PR is this?
/kind bug

What this PR does / why we need it:
Improve the controller performance by skipping the reconcile when spec does not change

Which issue(s) this PR fixes:

Fixes #

Requirements:

• run make reviewable for basic local test
• Read and followed fleet-networking's Code of conduct.
• uses conventional commit messages
• includes documentation
• adds unit tests

How has this code been tested

e2e tests passed, https://github.com/Azure/fleet-networking/actions/runs/16045339812/job/45280756357

Special notes for your reviewer

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.31%. Comparing base (ef018fe) to head (30f0ebc).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #317      +/-   ##
==========================================
- Coverage   80.48%   80.31%   -0.17%     
==========================================
  Files          29       29              
  Lines        4161     4161              
==========================================
- Hits         3349     3342       -7     
- Misses        647      650       +3     
- Partials      165      169       +4     

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