feat: add Spring AI MCP tool adapter

[zgzyq]

Describe what this PR does / why we need it

Adds a transport-independent Spring AI MCP adapter that protects individual
tool calls with Sentinel. MCP transports share fixed endpoints, so URL-level
WebMVC/WebFlux interception cannot distinguish tools. Decorating tool
specifications creates stable resources such as mcp:tool:echo.

Does this pull request fix one issue?

Fixes #3581

Describe how you did it

• add a Java 17 adapter module based on Spring AI 2.0.1 and MCP Java SDK 2.0.0
• decorate stateful and stateless synchronous/asynchronous tool specifications
• create inbound COMMON_RPC entries per tool and trace execution errors
• keep async entries open until completion, error, or cancellation
• guarantee every entered resource exits exactly once

Describe how to verify it

mvn -pl sentinel-adapter/sentinel-spring-ai-mcp-adapter -am test

The tests cover success, blocking, exception tracing, async completion,
cancellation, stateless tool specifications, and actual Sentinel flow rules.

Special notes for reviews

This intentionally leaves HTTP/SSE/WebMVC/WebFlux adapters unchanged. The
protection point is the MCP tool handler, so resource naming remains consistent
across transports.

[CLAassistant]

All committers have signed the CLA.

[oss-sentinel-ai]

CLA Not Signed

The Contributor License Agreement (CLA) check is currently pending on this PR (license/cla: Contributor License Agreement is not signed yet.). This PR cannot be merged until the CLA is signed.

@zgzyq please sign the CLA via the CLA assistant badge in the comment above, or visit https://cla-assistant.io/alibaba/Sentinel. Once signed, the license/cla status will turn green.

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[oss-sentinel-ai]

Summary

This PR adds a decorator for synchronous and reactive Spring AI MCP tool specifications, creating inbound COMMON_RPC Sentinel resources named mcp:tool:<tool-name>, tracing thrown failures, and retaining async entries through completion, error, or cancellation. Its lifecycle pairing and BlockException handling align with the existing Reactor adapter, and its Java 17 and local version conventions match existing optional adapter modules.

LGTM — code changes look good, but this PR cannot be approved/merged until the contributor signs the CLA (see the CLA reminder comment above). Once the CLA is signed, feel free to @mention me for a re-review.

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