fix: handle nil annotations in mse.lua

[AdeshDeshmukh]

What this PR does / why we need it

Added nil check for obj.annotations in mse.lua before using it. This follows the same pattern already used in higress.lua and prevents potential nil reference errors when annotations are not present.

Which issue(s) this PR fixes

Fixes #228

Changes made

Added nil handling for obj.annotations in lua_configuration/trafficrouting_ingress/mse.lua:

annotations = {}
-- obj.annotations is ingress annotations, handle nil case
if ( obj.annotations )
then
    annotations = obj.annotations
end

This matches the pattern used in higress.lua (line 1-6).

Testing done

• Verified the fix matches the pattern in higress.lua
• No other code changes needed

Does this PR introduce a user-facing change?

NONE

[kruise-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 51.38%. Comparing base (8416512) to head (aff7ebd).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #334   +/-   ##
=======================================
  Coverage   51.38%   51.38%           
=======================================
  Files          66       66           
  Lines        8559     8559           
=======================================
  Hits         4398     4398           
  Misses       3575     3575           
  Partials      586      586           

Flag	Coverage Δ
unittests	51.38% <ø> (ø)

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