feat: add support for detecting SELECT * in const and var declarations

[chelout]

Summary

Adds support for detecting SELECT * usage in const and var declarations at package and function levels.

Problem

Previously, the analyzer only detected SELECT * in:

• Short variable declarations: query := "SELECT * FROM users"
• Function call arguments: db.Query("SELECT * FROM users")

But missed a common pattern of storing SQL queries in constants:

const UserQuery = "SELECT * FROM users"  // ❌ Not detected
var OrderQuery = "SELECT * FROM orders"  // ❌ Not detected

Solution

Core Changes

• Added checkGenDecl() function to process *ast.GenDecl nodes (const/var declarations)
• Integrated into both entry points: run() and RunWithConfig()
• Now detects:
  • ✅ Package-level constants: const Query = "SELECT * FROM users"
  • ✅ Package-level variables: var Query = "SELECT * FROM users"
  • ✅ Declaration blocks: const (...) and var (...)
  • ✅ Local constants inside functions

Documentation Updates

• Updated README.md with new feature description
• Added examples for constants and variables

Examples

❌ Will be detected:

const QueryUsers = "SELECT * FROM users"
var DynamicQuery = "SELECT * FROM logs"

const (
    GetAllUsers = "SELECT * FROM users"
    GetOrders   = "SELECT * FROM orders"
)

func example() {
    const localQuery = "SELECT * FROM categories"
}

✅ Good practices:

const GoodQuery = "SELECT id, name, email FROM users"
const CountQuery = "SELECT COUNT(*) FROM users"
const SchemaQuery = "SELECT * FROM information_schema.tables"

Technical Details

AST Analysis confirms no duplication:

• checkAssignStmt handles *ast.AssignStmt: short declarations (:=) and assignments (=)
• checkGenDecl (new) handles *ast.GenDecl: const and var declarations
• Functions are complementary with no overlap