Add local variable resolution and attribute rendering to handler

- Add resolve_value helper: checks local_vars first, then global state
- Add evaluate_condition helper: merges local vars into state for
  condition evaluation
- Fix process_for_loop to resolve collections from local vars
  (enables nested for loops like outerItem.innerItems)
- Fix process_attribute to resolve values from local vars and handle
  numeric/bool types properly
- Fix process_if to evaluate conditions against merged local+global state
- Simplify process_signal to delegate to resolve_value

13 new tests: boolean attrs (true/false/missing/multiple), simple attrs
(string/numeric), template attrs, raw signals, nested for loops,
for+if state scoping. 20 total handler tests.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: mohamedmansour