Make Ident enum

Ident now is a struct with a quote style:
```
pub struct Ident {
pub value: String,
pub quote_style: Option,
```
Now it is a bit risky, because if the char isn't the expected it panics:
```
assert!(quote == '\'' || quote == '"' || quote == '`' || quote == '[');
```
Now it is true that it shouldn't never get to it, because when we tokenize we are only allowing those to be the quote style, but it is still risk for panics.

I suggest to move Ident to be an enum:
```
pub enum Ident {
Literal(String),
SingleQoute(String),
DoubleQoute(String)
...
}
```
Now the Display will be:
```
impl fmt::Display for Ident {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
match self {
Literal(value) => write!(f, "{}", value),
SingleQoute(value) => write!(f, "'{}'", value),
...
}
}
```
And we can also implement a method `get_value`:
```
impl Ident {
fn get_value(&self) -> String {
match self {
Literal(value) | SingleQoute(value) ... => return value.clone()
}
}
```

If it is acceptable I will add a PR with the code

Start by locating the Ident struct, its Display implementation, and the tokenizer assertion that validates quote_style. Trace all uses of Ident.value and quote_style before deciding how the enum variants should replace them. Done means invalid quote styles can no longer reach a panic and the parser’s existing behavior is preserved.

Written by the indexing model from the issue text.