fix(mcp): migrate to MCP SDK 0.18.3 JSON APIs

[skrcode]

What is the purpose of the change?

This companion PR completes the MCP SDK 0.18.3 upgrade in #16342. The SDK replaced its Jackson-specific APIs with McpJsonMapper/TypeRef and removed the deprecated string-schema Tool constructors, leaving the Dependabot head unable to compile.

The change:

• adapts Dubbo's existing ObjectMapper instances through the SDK-provided JacksonMcpJsonMapper;
• uses the SDK's new TypeRef transport contract;
• migrates tool creation to the mapper-aware builder, preserving the previous JSON Schema parsing behavior;
• removes a redundant Mockito @InjectMocks path that constructed the SSE provider with a null mapper before the test's explicit setup; and
• carries the already merged test-isolation fix from fix: make SpringBootConfigPropsTest immune to leaked metrics System properties #16420 onto this older Dependabot branch. Without that fix, all five unit-test jobs fail because leaked dubbo.metrics.* System properties override the Spring test's Prometheus configuration.

No public API or MCP wire behavior is intentionally changed.

Verification

• Reproduced 8 Java compilation errors on exact Dependabot head 09795dcd58e0137c63ea5307b025893cd1aa0c48 with ./mvnw -pl dubbo-plugin/dubbo-mcp -DskipTests compile.
• Confirmed the five red GitHub jobs all fail at SpringBootConfigPropsTest with expected: <prometheus> but was: <disabled>, then traced the exact defect to the maintainer-approved and merged fix: make SpringBootConfigPropsTest immune to leaked metrics System properties #16420.
• Ran SpringBootConfigPropsTest and SpringBootMultipleConfigPropsTest while deliberately injecting -Ddubbo.metrics.protocol=disabled -Ddubbo.metrics.enabled=false; both passed with the accepted isolation fix.
• ./mvnw -T 4 -pl dubbo-plugin/dubbo-mcp -am clean install -DskipTests ... — all 53 reactor modules compiled, packaged, and installed successfully on JDK 17.
• ./mvnw -pl dubbo-plugin/dubbo-mcp clean test verify -Pjacoco,... — all 89 MCP tests passed and the JaCoCo report was generated on JDK 17.
• git diff --check passed.

Checklist

• Make sure there is a GitHub_issue field for the change. (Dependency-upgrade context: build(deps): bump io.modelcontextprotocol.sdk:mcp from 0.11.2 to 0.18.3 #16342.)
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit-test to verify your logic correction. Existing transport and tool-schema tests exercise the migrated paths; the SDK-dependent fixture was updated.
• Make sure GitHub Actions can pass. Why the workflow is failing and how to fix it?

[codecov-commenter]

Codecov Report

❌ Patch coverage is 72.41379% with 8 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (dependabot/maven/io.modelcontextprotocol.sdk-mcp-0.18.3@09795dc). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...transport/DubboMcpStreamableTransportProvider.java	40.00%	6 Missing ⚠️
...bo/mcp/transport/DubboMcpSseTransportProvider.java	71.42%	2 Missing ⚠️

Additional details and impacted files

@@                                    Coverage Diff                                     @@
##             dependabot/maven/io.modelcontextprotocol.sdk-mcp-0.18.3   #16442   +/-   ##
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  Coverage                                                           ?   60.82%           
  Complexity                                                         ?    11769           
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  Files                                                              ?     1953           
  Lines                                                              ?    89219           
  Branches                                                           ?    13458           
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  Hits                                                               ?    54268           
  Misses                                                             ?    29389           
  Partials                                                           ?     5562           

Flag	Coverage Δ
integration-tests-java21	32.19% <0.00%> (?)
integration-tests-java8	32.24% <0.00%> (?)
samples-tests-java21	32.19% <0.00%> (?)
samples-tests-java8	29.77% <0.00%> (?)
unit-tests-java11	59.09% <ø> (?)
unit-tests-java17	58.52% <72.41%> (?)
unit-tests-java21	58.56% <72.41%> (?)
unit-tests-java25	58.53% <72.41%> (?)
unit-tests-java8	59.08% <ø> (?)

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