Colon as operator part at beginning of line in REPL

## Compiler version

3.7.3, 3.8.0-RC1-bin-20251007-71fcd1a-NIGHTLY

## Minimized code

In REPL:

```scala
::(1, Nil)
```

## Output

```scala
Unknown command: "::(1,", run ":help" for a list of commands
```

## Expectation
 This should be evaluated as it is when not typed at the very beginning of a line in REPL (e.g. like ` ::(1, Nil)` with a leading white space)

