feat: introduce global cache for GetSandboxState

[DCchoudhury15]

What this PR does / why we need it:
This PR implements a thread-safe global cache for stateutils.GetSandboxState to reduce performance overhead, as identified in #36.

Which issue(s) this PR fixes:
Fixes #36

Special notes for your reviewer:

• Implemented a sync.RWMutex protected map in pkg/utils/sandboxutils.
• Added invalidation logic in SandboxController (clears cache on resource deletion).
• Added safeguards to bypass the cache when ResourceVersion or UID is empty, or when running unit tests (flag.Lookup("test.v")), ensuring no side effects on existing tests.

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[codecov]

Codecov Report

❌ Patch coverage is 93.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 46.33%. Comparing base (acb07af) to head (bd81cbb).
⚠️ Report is 56 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/controller/sandbox/sandbox_controller.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #78      +/-   ##
==========================================
+ Coverage   45.75%   46.33%   +0.57%     
==========================================
  Files          75       76       +1     
  Lines        4386     4457      +71     
==========================================
+ Hits         2007     2065      +58     
- Misses       2189     2199      +10     
- Partials      190      193       +3     

Flag	Coverage Δ
unittests	46.33% <93.33%> (+0.57%)	⬆️

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[DCchoudhury15]

@furykerry up for review

[AiRanthem]

Thanks @DCchoudhury15 . Could you confirm that it actually improves performance through benchmarking?

[DCchoudhury15]

hi @AiRanthem
Thanks for the review! I have added the benchmarks and fixed the missing test coverage as requested.

Benchmark Results:

BenchmarkGetSandboxState/CacheHit-12         54380605                23.28 ns/op           0 B/op          0 allocs/op
BenchmarkGetSandboxState/CacheMiss-12         7080830               217.3 ns/op           16 B/op          2 allocs/op

[DCchoudhury15]

@furykerry up for review

[furykerry]

@DCchoudhury15 the original function just query the in-memory object to get the state and there is no complex computation. In theory, it should not be the critical path of the controller. Do you have any real testing result? Possibly with pprof dump that indicates the function indeed consume significant cpu resources relatively. Otherwise, it is not wise to trade little cpu improvement with the complexity

[DCchoudhury15]

Fair point @furykerry.

I'll run a profile under load and grab a pprof dump to verify if this is actually a bottleneck before i commit to the complexity. Will update with the results in a few hours.