feat(c++): make fory enum/nuion macro in user namespace

[chaokunyang]

Why?

Allow C++ enum/union/field metadata macros to live in user namespaces (no forced fory:: specialization) while keeping registration/serialization behavior consistent.

What does this PR do?

• Switch C++ enum/field/union metadata to ADL-based descriptors and update union serialization to use UnionInfo (case ids, metas, factories).
• Adjust C++ codegen to emit namespace-scope macros and clean up union/field generation details.
• Add a namespace macro test and wire it into C++ serialization build/test targets.
• Update C++ docs to clarify scope rules (FORY_ENUM at namespace scope, FORY_STRUCT in public scope).
• Set FORY_JAVASCRIPT_JAVA_CI=0 in the JavaScript xlang CI job.

Related issues

#3099
#2906
#1017

Does this PR introduce any user-facing change?

C++ macro placement rules are now enforced via ADL-based descriptors; docs call out the required scope for FORY_ENUM/FORY_STRUCT.

• Does this PR introduce any public API change?
• Does this PR introduce any binary protocol compatibility change?

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