fix(graph): preserve RunnableConfig context in compiled subgraph

[OiPunk]

Describe what this PR does / why we need it

This PR fixes context propagation for compiled subgraphs. RunnableConfig.context is meant to carry per-run mutable data across nodes, but SubCompiledGraphNodeAction cleared context before invoking the compiled subgraph, causing data loss.

Does this pull request fix one issue?

Fixes #4191

Describe how you did it

• Removed subGraphRunnableConfig.clearContext() in SubCompiledGraphNodeAction so subgraph execution keeps parent run context.
• Added regression test testCompiledSubGraphShouldInheritRunnableContext in CompiledSubGraphTest.
  • Parent node writes trace_id into RunnableConfig.context.
  • Subgraph node reads the same key and emits it in output.
  • Test verifies expected output includes [SUB:ctx-123].

Describe how to verify it

Run:

• JAVA_HOME=/usr/local/opt/openjdk@17/libexec/openjdk.jdk/Contents/Home ./mvnw -pl spring-ai-alibaba-graph-core -am test

Result:

• Tests run: 277, Failures: 0, Errors: 0, Skipped: 52

Special notes for reviews

• Change scope is limited to compiled-subgraph runnable config handling and one focused regression test.
• No API changes.