Function detect_repl_continuation_mode 

pub fn detect_repl_continuation_mode(source: &str) -> ReplContinuationMode

Available on crate features code and embedded-python only.

Detects whether REPL source is complete or needs more input.

This mirrors CPython’s broad interactive behavior:

• Incomplete bracketed / parenthesized / triple-quoted constructs continue.
• Clause headers (if:, def:, etc.) require an indented body and then a terminating blank line before execution.
• All other parse outcomes are treated as complete (either valid code or a syntax error that should be shown immediately).