test: cover printable typeof on sumtypes

[vincenzopalazzo]

Summary

• add regression coverage for using raw typeof(sumtype) as a printable string expression
• lock in the behavior reported in Printing typeof() fails to compile #26704 without changing current cgen logic

Root cause

The original issue was a codegen regression in older compiler builds when println(typeof(step)) was used on a sumtype. The current tree no longer reproduces that failure, but there was no targeted test covering that path.

Verification

• ./vnew -gc none -silent vlib/v/tests/typeof_test.v
• ./vnew -g -o /tmp/issue26704_pr.c /tmp/issue26704_pr.v
• ./vnew -gc none /tmp/issue26704_pr.v && /tmp/issue26704_pr

Fixes #26704

[JalonSolov]

Close/re-open for CI run.

[JalonSolov]

A conflict to resolve, and a problem with typeof to be fixed (shows in the diff view).

[vincenzopalazzo]

Fixed in dbeba19. The PR diff is back to vlib/v/tests/typeof_test.v only, and the regression now exercises println(typeof(...)) directly while asserting the raw typeof values without the helper.

Verified with ./vnew -gc none -silent vlib/v/tests/typeof_test.v.

[JalonSolov]

Still failing CI with:

Error: vlib/v/tests/typeof_test.v:132:10: error: use e.g. `typeof(expr).name` or `sum_type_instance.type_name()` instead

[vincenzopalazzo]

Trying with 7e62c50