[ICE] Ternary operator in let binding causes compiler crash

Fe version: 0.26.0
Description: When using a ternary operator (?:) inside a let binding, the Fe compiler crashes.

```
contract C {
pub fn f(self, b: u256) -> u256 {
require(b < 10);
let c: u256 = b < 5 ? 5 : 1; // ❌ This line triggers compiler crash
let d: u256 = c > 5 ? 3 : 2;
return d;
}
}
```
```
thread 'main' panicked at crates/parser/src/lexer/token.rs:313:22:
internal error: entered unreachable code
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

You've hit an internal compiler error. This is a bug in the Fe compiler.
Fe is still under heavy development, and isn't yet ready for production use.

If you would, please report this bug at the following URL:
https://github.com/ethereum/fe/issues/new
```

Reproduce the crash with the contract example, then inspect crates/parser/src/lexer/token.rs around line 313 and trace the token handling reached by the ternary expression in a let binding. Done means the example compiles without the reported internal compiler error.

Written by the indexing model from the issue text.