Function lookup

lookup(ident: string): Token
Returns the token type that corresponds to a given string.

This function is used by the lexer to classify identifiers and keywords. If the string is a reserved keyword, it returns the appropriate token type. Otherwise, it returns Token.Id to indicate a user-defined identifier.
Parameters
- ident: string
  The string to look up
Returns Token
The corresponding token type
Example: Keyword lookup
```
lookup('qubit');     // Returns Token.Qubit
lookup('measure');   // Returns Token.Measure
lookup('myVar');     // Returns Token.Id
lookup('π');         // Returns Token.Pi
```
- Defined in src/qasm3/token.ts:372