feat: add --mode and --operators flags to mutation testing tools

[ctoyan]

Implements configurable mutation operator modes (light, medium, heavy) based on operator effectiveness analysis (22,597 mutants across Aptos' Move framework). This allows users to trade off speed vs thoroughness when running mutation tests. It also allows to add different operators that we support, per operator basis.

Motivation

Running full mutation testing with all operators can be time-consuming.
This PR enables faster feedback loops by allowing users to run only the most effective operators or custom ones that they want to test for.

Changes

New Module: operator_filter.rs

• OperatorMode enum with Light, Medium, Heavy, and Custom variants
• Operator effectiveness constants with validation
• Mode filtering logic applied at mutant generation time

CLI Additions

Both move-mutator and move-mutation-test now support:

--mode <light|medium|heavy> - Predefined operator sets

• light: unary_operator_replacement, delete_statement, break_continue_replacement
• medium: light + binary_operator_replacement, if_else_replacement
• heavy (default): medium + literal_replacement, binary_operator_swap

--operators <op1,op2,...> - Custom operator selection

• Comma-separated list of specific operators
• Validates operator names and aborts on invalid input
• Mutually exclusive with --mode

Implementation Details

• Filtering happens at mutant creation in parse_expression_and_find_mutants() to avoid wasted computation
• Configuration validates and parses modes at startup
• Displays active mode and enabled operators for transparency
• Default behavior unchanged (Heavy mode) for backward compatibility

Usage Examples

# Light mode - fastest execution (3 operators)
move-mutation-test run --mode light

# Medium mode - balanced (5 operators)
move-mutation-test run --mode medium

# Custom selection
move-mutation-test run --operators unary_operator_replacement,delete_statement

[joske]

Very nice! 🔥