fix: math and redirect issues

[cjbell]

Summary

Fixed:

• Single-digit redirect parsing: Numbers before redirects with whitespace (echo 1 > file) are now correctly parsed as arguments
• Division by zero: Now properly errors like bash does
• Hex/octal escapes: Both echo -e and $'...' now properly interpret \xNN and \NNN escapes
• Heredoc tab stripping: <<- now strips leading tabs from content
• Group redirections: { cmd; } &>/dev/null now works correctly