follow-up: replace `?` operator in for-loops with `if let Some` in verilog extractor

[carlos-alm]

Deferred from PR #1107 review.

Original reviewer comment: #1107 (comment)

Context: Greptile flagged that several handlers in crates/codegraph-core/src/extractors/verilog.rs use node.child(i)? inside for loops. The ? operator exits the entire loop on the first None instead of continuing past it. In practice this is harmless today because child_count always returns valid indices, but if let Some(child) = node.child(i) is more defensively correct and consistent with handle_package_import / handle_include_directive. A sweep would touch several handlers — this issue tracks doing the cleanup as one cohesive PR rather than mixing it with #1107.