Fix directory execution, nested tab-completion quoting, and zero-argument source evaluation

[toumorokoshi]

This PR addresses multiple issues regarding command execution logic, help parameter formatting, and shell argument inheritance in tome.

Changes Included:

1. Directory execution correctly outputs helpful listings

   • Directory paths parsed via CommandType::Execute now evaluate to a help::help string instead of returning a generic error indicating the user executed a directory. Effectively, executing a directory is treated the same as invoking my_cmd help on that directory context natively.
   • Addressed parameter formatting positions in commands/help.rs for help_all_in_dir, which originally wrongly substituted the output templates.

2. Tab completions successfully split nested directories

   • In commands/init.rs, the expansion argument passed into command-complete ... "$tome_args" caused bash array parameters broken by spaces to be wrapped collectively into a single argument value array block. Removed quotes ($tome_args) so complete expands array params natively line-by-line enabling nested script evaluation.

3. Restored proper Argument inheritance isolation for sourced scripts

   • Bash and zsh natively inherit shell-level outer-arguments inside source blocks if no parameters are supplied. When executing source file.source on a zero-length argument base, .source accidentally inherited the script context bounds (e.g. $1=script_name).
   • Bound set --; via string formatting directly onto CommandType::Execute paths under tome/src/script.rs whenever targeted length maps to exactly zero on valid source scripts (Only within bash/zsh).
   • Refactored generic sourcing unit tests in src/lib_tests.rs to validate positional parameters clearing via set --; .