Fix string literal escaping and allow variable-width runtime state

[someone235]

This change makes SilverScript string literals follow JSON escape semantics and allows portable artifacts to contain canonically encoded variable-width runtime state.

Language Behavior Changes

• String literals must now use double quotes. Single-quoted strings are no longer accepted.

string valid = "It's working";
// string invalid = 'text';

• Escape sequences are decoded using JSON semantics, including escaped quotes, backslashes, control characters, Unicode escapes, and surrogate pairs. Malformed or unsupported escapes are
  rejected.

string message = "line 1\nline 2";
string quoted = "She said \"hello\"";
string path = "left\\right";
string unicode = "\u6771";

• Formatting SilverScript produces canonical double-quoted strings without changing their decoded bytes. In particular, a literal backslash followed by a quote remains distinct:

string constant VALUE = "\\\"";

• Portable ABI artifacts now accept canonically encoded variable-width runtime state, including strings, dynamic byte arrays, and dynamic arrays with decodable elements.

contract VariableState(string initial) {
    string stored = initial;

    entry main() {
        require(stored == "hello");
    }
}

Compiler and CLI artifacts containing this state can now be verified and consumed normally.