Phase 116: std::span Integration - Dyndata accessors

Added std::span accessors to Dyndata class for improved type safety
and modern C++ idioms.

Changes:
- Added Dyndata::actvarGetSpan() methods (const and non-const overloads)
- Returns std::span<Vardesc> for the actvar array
- Complements existing pointer-based accessors

Context:
- Phase 112 already added Proto span accessors (code, constants, protos, upvalues)
- Phase 115.1 added std::span to buffer/string operations
- Phase 115.3 added Table::getArraySpan()
- Phase 116 completes span integration for compiler data structures

Performance Results:
- Baseline: 4.20s avg
- Current:  4.18s avg (5-run benchmark)
- Change:   -0.5% (maintained)
- Target:   ≤4.33s ✅ PASS

Benefits:
- Zero-cost abstraction
- Better type safety (no raw pointer arithmetic)
- Enables range-based algorithms
- Modern C++23 idioms

All tests passing with "final OK !!!"

Author: claude

src/compiler/lparser.h

@@ -7,6 +7,7 @@
 #ifndef lparser_h
 #define lparser_h
 
+#include <span>
 #include "llimits.h"
 #include "lobject.h"
 #include "lopcodes.h"
@@ -277,6 +278,14 @@ class Dyndata {
     return &actvar_vec.back();
   }
 
+  /* Phase 116: std::span accessors for actvar array */
+  inline std::span<Vardesc> actvarGetSpan() noexcept {
+    return std::span(actvar_vec.data(), actvar_vec.size());
+  }
+  inline std::span<const Vardesc> actvarGetSpan() const noexcept {
+    return std::span(actvar_vec.data(), actvar_vec.size());
+  }
+
   /* Legacy accessor interface for backward compatibility */
   class ActvarAccessor {
   private: