feat: dynamic argument substitution and placeholders

[Jintin]

This PR adds support for dynamic arguments in aliases without breaking the existing storage format.

Features

• Append: If no placeholders are used, arguments are appended to the end of the command.
• Global Fill (?): The ? placeholder is replaced by all provided arguments.
• Positional Fill (?1, ?2...): Placeholders like ?1 and ?2 are replaced by the corresponding positional arguments.

Improvements

• No changes to the ~/.aliasme/cmd format; existing aliases continue to work perfectly.
• Proper handling of arguments with spaces using eval and $*/$@.
• Updated help menu with documentation for the new features.
• Comprehensive new test suite in test/aliastest.sh.