feat: snip all chained commands instead of only the first one

[VincentHardouin]

Closes #3

Summary

• Refactor toolExecuteBefore to split commands on all shell operators (&&, ||, ;, &, |) and apply snip to each segment individually instead of only the first command.
• Extract a reusable snipCommand() helper function.
• Update existing tests for &&, |, ; and add 4 new test cases (||, &, mixed operators, env vars with &&).
• Fix cd /tmp && ls to skip cd but still snip ls.