Function parse_slash_commands 

pub fn parse_slash_commands(diff: &str) -> Vec<String>

Extract slash commands from user-added lines in a unified diff.

Guards against false positives:

• Lines inside code fences (``` or ~~~) are excluded.
• Blockquote lines (starting with >) are excluded.
• Only lines added by the user (+ prefix, not +++) are inspected.
• The command must start with / followed immediately by an ASCII letter.

Returns the trimmed command strings (including any arguments after the command).