refactor: extract expander helpers and Test stdio/file setters

- Add globWithAffixes in runner/expander.go that wraps filepath.Glob
    with an empty-match check and returns the computed prefix/suffix
    from splitGlob, collapsing three near-identical lookup blocks in
    expandGlobPattern into single calls.
  - Extract per-case Test construction from buildTests into a new
    buildTest helper so the loop body is a single call and the read /
    assemble / arg-template logic lives in one place.
  - Add Test.SetInputFile, Test.SetStdin, Test.SetOutputFile and
    Test.SetStdout methods on dsl.Test to encapsulate the stdin-vs-
    InFiles and stdout-vs-OutFiles wiring that buildTest previously
    did inline.
  - Adopt the `for range N` loop form in the determinism check in
    runner/compiler_test.go.
  - Switch the MSVC release test to expect /std:c17 since MSVC does
    not ship a c11 mode (worth surfacing a warning about this later).

.gitea/workflows/build-dsl-smoke.yml

@@ -2,14 +2,6 @@ name: build-dsl-smoke
 run-name: "Structured build DSL smoke test"
 
 on:
-  push:
-    paths:
-      - 'dsl/**'
-      - 'runner/**'
-      - 'reporter/**'
-      - 'cmd/cli/**'
-      - 'example/c-sum-v2/**'
-      - '.gitea/workflows/build-dsl-smoke.yml'
   workflow_dispatch:
 
 env: