refactor: improve variable naming throughout codebase

[EmperorOrokuSaki]

Issue

Several variables throughout the codebase use unclear or abbreviated names that reduce code readability.

Current State

Examples of unclear variable names:

• static_jump_targets → should be discovered_jump_targets
• valid_pcs → should be valid_program_counters
• prev_instr → should be previous_instruction
• doms → should be dominators
• post → should be post_dominators
• pc_map → should be program_counter_mapping

Proposed Solution

Rename variables to use descriptive, full names that clearly indicate their purpose and content.

Benefits

• Improved code readability
• Self-documenting code
• Easier for new contributors to understand
• Better IDE support and autocomplete

Files to Modify

• crates/core/src/cfg_ir.rs
• crates/analysis/src/metrics.rs
• crates/transforms/src/shuffle.rs

Priority

Low - Code quality improvement