Fix test discovery for ingots where lib.fe has no tests - #1304

Summary

• run_tests_ingot only checked the root module (lib.fe) for #[test] functions via has_test_functions(db, root_mod). If lib.fe contained no tests, the entire ingot was silently skipped with "No tests
  found" — even when other modules had tests.
• Add ingot_has_test_functions that checks all modules in the ingot via Ingot::all_funcs, and use it in place of the root-module-only check.
• Add a regression test with an ingot fixture whose lib.fe has no tests while a sibling module (helper.fe) does.

Reproduction

Create an ingot where lib.fe only exports helpers and all #[test] functions live in other modules:

src/lib.fe ← pub fn add(a: u256, b: u256) -> u256 { ... } (no tests)
src/helper.fe ← #[test] fn test_add() { ... }

$ fe test .
Warning: No tests found in .

After this fix, fe test correctly discovers and runs test_add.

Test plan

• New test test_cli_test_ingot_discovers_tests_in_non_root_modules passes with fix, fails without
• All existing fe_test / fe_test_runner tests pass (49/49)