Function validate_invariants 

pub fn validate_invariants(
    before: &GraphSnapshot,
    after: &GraphSnapshot,
) -> Result<Vec<InvariantCheck>>

Validate that refactoring invariants are preserved.

Checks:

• Reference counts are preserved (same number of incoming/outgoing edges)
• No orphaned symbols (all symbols remain reachable from entry points)
• Symbol IDs are stable (no new IDs generated, only name changes)
• Entry points are preserved (no loss of public API)

Arguments

• before - Graph snapshot before refactoring
• after - Graph snapshot after refactoring

Returns

A vector of invariant check results, one for each invariant validated.