Fix NAOCS close client bug

[mlboy]

Greptile Summary

This PR corrects the Nacos resolver shutdown lifecycle:

• Retains subscription parameters so the resolver can unsubscribe during shutdown.
• Cancels endpoint processing, unsubscribes, closes the naming client, and drains pending callback data.
• Buffers the callback channel to reduce shutdown-time blocking.
• Restores the canonical Go module path following the previous review.

Confidence Score: 5/5

The PR appears safe to merge, with no outstanding correctness, security, or repository-rule issues identified.

The previously reported module-path mismatch is fully fixed by restoring the canonical github.com/zeromicro/zero-contrib/zrpc/registry/nacos declaration, and no new actionable issues were introduced by that correction.

Important Files Changed

Filename	Overview
zrpc/registry/nacos/builder.go	Builds a buffered callback pipeline and retains the Nacos client and subscription parameters for orderly shutdown.
zrpc/registry/nacos/resolver.go	Makes resolver closure idempotently cancel processing, unsubscribe, close the client, and drain pending callback data.
zrpc/registry/nacos/resolver_test.go	Updates the test client and watcher tests for the new unsubscribe-aware resolver lifecycle.

Sequence Diagram

sequenceDiagram
    participant Resolver
    participant Context
    participant Nacos
    participant Pipe
    Resolver->>Context: cancel()
    Resolver->>Nacos: Unsubscribe(subParam)
    Resolver->>Nacos: CloseClient()
    Resolver->>Pipe: drain pending callback data

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_{Reviews (3): Last reviewed commit: "Fix nacos module path" | Re-trigger Greptile}