Refactor to use format for http responses

style.md

@@ -102,6 +102,27 @@ auto addr = reinterpret_cast<uintptr_t>(ptr);         // Pointer to integer conv
 - **String views** with `std::string_view` to minimize unnecessary copying
 - **Arena allocation** for efficient memory management (~1ns vs ~20-270ns for malloc)
 
+### String Formatting
+- **Always use `format.hpp` functions** - formats directly into arena-allocated memory
+- **Use `static_format()` for performance-sensitive code** - faster but less flexible than `format()`
+- **Use `format()` function with arena allocator** for printf-style formatting
+```cpp
+// Most performance-sensitive - compile-time optimized concatenation
+std::string_view response = static_format(arena,
+    "HTTP/1.1 ", status_code, " OK\r\n",
+    "Content-Length: ", body.size(), "\r\n",
+    "\r\n", body);
+
+// Printf-style formatting - runtime flexible
+ArenaAllocator& arena = conn.get_arena();
+std::string_view response = format(arena,
+    "HTTP/1.1 %d OK\r\n"
+    "Content-Length: %zu\r\n"
+    "\r\n%.*s",
+    status_code, body.size(),
+    static_cast<int>(body.size()), body.data());
+```
+
 ### Complexity Control
 - **Encapsulation is the main tool for controlling complexity**
 - **Header files define the interface** - they are the contract with users of your code