feat: optimize nacos discovery with privileged agent and LRU cache

[9268]

Description

This PR fixes a performance issue introduced by #12353 where all worker processes were fetching nacos service discovery information, causing unnecessary network requests and JSON parsing overhead per requests.

Changes made:

1. Restricted nacos discovery to privileged agent only - Only the privileged agent process now fetches service information from nacos servers
2. Added LRU cache optimization - Worker processes use version-controlled LRU cache to avoid repeated JSON parsing
3. Improved performance - Reduced shared memory access and eliminated redundant JSON decoding

Performance improvements:

• Eliminates duplicate nacos API calls from multiple worker processes
• Reduces JSON parsing overhead through LRU caching
• Maintains data consistency through version control mechanism

Which issue(s) this PR fixes:

Fixes #12353

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)

[Copilot]

Pull request overview

This PR optimizes Nacos service discovery by moving registry fetch work to the privileged agent process and introducing a version-controlled per-worker LRU cache to reduce repeated JSON decoding.

Changes:

• Restrict Nacos registry fetching timers to the privileged agent process only.
• Add a per-worker LRU cache for decoded node lists keyed by a shared-dict “version”.
• Store and manage per-service #version entries in the nacos shared dict to drive cache invalidation.

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[Baoyuantop]

Hi @9268, please fix failed CI

[9268]

@Baoyuantop hi,ci has been fixed https://github.com/9268/apisix/actions/runs/21792352299

[9268]

a code lint issue has been fixed;

[9268]

@Baoyuantop
It seems that the error in the GitHub Actions is a compilation error, and this PR does not involve that part. Could you please rerun the failing part? In my fork's branch, the GitHub Actions succeeded except for the Changelog check. https://github.com/9268/apisix