feat: Implement compiler and virtual machine for Fig language

- Added Compiler class with methods for compiling programs, statements, and expressions.
- Introduced Proto structure to hold compiled bytecode and constants.
- Implemented expression compilation including literals, identifiers, and infix expressions.
- Developed statement compilation for variable declarations and expression statements.
- Created a VM class to execute compiled bytecode with support for arithmetic and comparison operations.
- Added Object and Value classes for handling different data types and memory management.
- Implemented String and Struct objects for enhanced data representation.
- Established a parser for parsing variable declarations and statements.
- Included tests for the VM and object representations.

src/Compiler/StmtCompiler.cpp

@@ -0,0 +1,58 @@
+/*!
+    @file src/Compiler/StmtCompiler.cpp
+    @brief 编译器实现(语句部分)
+    @author PuqiAR (im@puqiar.top)
+    @date 2026-02-19
+*/
+
+#include <Compiler/Compiler.hpp>
+
+namespace Fig
+{
+    Result<void, Error> Compiler::CompileVarDecl(VarDecl *varDecl)
+    {
+        const String &name = varDecl->name;
+        if (HasLocalInCurrentScope(name))
+        {
+            return std::unexpected(Error(ErrorType::RedeclarationError,
+                std::format("variable `{}` has already defined in this scope", name),
+                "change its name",
+                makeSourceLocation(varDecl)));
+        }
+        std::uint8_t varReg;
+        if (varDecl->initExpr)
+        {
+            const auto &result = CompileExpr(varDecl->initExpr);
+            if (!result)
+            {
+                return std::unexpected(result.error());
+            }
+            std::uint8_t resultReg = *result;
+            varReg                 = resultReg; // 复用临时计算结果寄存器
+            DeclareLocal(varDecl->isPublic, name, varReg);
+        }
+        else
+        {
+            varReg = DeclareLocal(varDecl->isPublic, name);
+        }
+        return Result<void, Error>();
+    }
+    Result<void, Error> Compiler::CompileStmt(Stmt *stmt) // 编译语句
+    {
+        if (stmt->type == AstType::ExprStmt)
+        {
+            ExprStmt   *exprStmt = static_cast<ExprStmt *>(stmt);
+            Expr       *expr     = exprStmt->expr;
+            const auto &result   = CompileExpr(expr);
+            if (!result)
+            {
+                return std::unexpected(result.error());
+            }
+        }
+        else if (stmt->type == AstType::VarDecl)
+        {
+            return CompileVarDecl(static_cast<VarDecl *>(stmt));
+        }
+        return Result<void, Error>();
+    }
+}; // namespace Fig