v1.2.3

release: v1.2.3 - CTE & UNION fluent builders
🎯 Core Theme: Composable SQL pipelines without leaving BuilderX

✨ New Capabilities:

1. Common Table Expressions

   • With(name, fn) & WithRecursive(name, fn) for multi-stage query setup
   • Automatic alias normalization and parameter propagation
   • Regression coverage via with_cte_test.go

2. UNION chaining

   • UNION(kind, fn) with ALL() helper (default = DISTINCT)
   • Stack multiple unions while preserving ORDER BY / LIMIT semantics
   • New tests ensure DISTINCT/ALL correctness

3. Metadata injection

   • Meta(func(meta *interceptor.Metadata)) enables inline TraceID/Tenant setup
   • Interceptors receive enriched metadata prior to Build()

🔧 Internal Improvements:

• Shared SQL core writer now feeds both base SELECT and UNION branches
• DISTINCT constant renamed to DISTINCT_SCRIPT to avoid helper collision
• Builder states cache CTE / UNION clauses to avoid duplicate builds

📖 Documentation:

• README updated with v1.2.3 highlight section, CTE/UNION examples, metadata usage
• CHANGELOG、Release Notes、Test Report 全面同步

🧪 Quality:

• go test ./... ✅ (~240 cases including new suites)
• No breaking changes; existing APIs continue to work unchanged

🚀 Summary:
v1.2.3 brings enterprise-grade analytics features—CTEs, recursive hierarchies, UNION composition, and observability—while keeping the fluent builder experience intact.