Match expressions with nested constructor patterns (e.g.
Cons(Some(@int), _)) now compile to WASM correctly. Previously
any ConstructorPattern or NullaryPattern sub-pattern caused the
function to be silently skipped (return None at L347).

Changes to vera/wasm/data.py:
- _collect_nested_tag_checks: recursively emits tag comparisons
  for nested constructors, AND-chained into the arm condition
- _extract_constructor_fields: recursively loads nested field
  pointers and binds their sub-patterns (ConstructorPattern),
  or advances offset for nullary (NullaryPattern)
- _sub_pattern_wasm_type: resolves WASM types for offset computation
- _translate_match_condition: integrates nested checks after
  outermost tag check

5 new tests, 1,337 total. examples/pattern_matching.vera first_some
now compiles and runs.

Co-Authored-By: Claude <noreply@anthropic.invalid>