test: expand dsl/runner coverage and add go-test CI workflow

- Add dsl/matcher_test.go covering ExactMatcher, ContainsMatcher,
    RegexMatcher, NumericEpsMatcher, AnyOrderMatcher and NoMatcher —
    previously 0% — including epsilon, count mismatch, unparsable
    numbers, invalid regex, and splitLines edge cases.
  - Add dsl/ast_test.go for the new Test.SetInputFile / SetStdin /
    SetOutputFile / SetStdout helpers and Pattern.IsDirMode.
  - Add dsl/build_string_test.go covering BuildProfile.String,
    WarningLevel.String and BuildConfig.MergeFrom (wrapper, defines
    into nil map, defines override existing, nil src).
  - Add dsl/merge_test.go driving mergeFiles to 100%: legacy build
    fields, duplicate toolchain/build/group from include, binary /
    sources / normalize_crlf / trim_trailing_ws propagation, local
    overrides of timeout and memory_limit.
  - Add dsl/parser_features_test.go for parseTest / parseGroup happy
    paths that were missing: file/outFile, env, wrapper, per-test
    timeout/memory overrides, non-zero exitCode, scoring partial /
    all_or_none and unknown scoring.
  - Add dsl/parser_errors_test.go, a 54-case table-driven test that
    hits every `expect(...)` error branch in parseGroup and parseTest
    (missing LPAREN/RPAREN/LBRACE/RBRACE/ASSIGN, wrong token types on
    weight/timeout/memory_limit/scoring/env/wrapper/file/outFile, and
    unclosed blocks).
  - Add dsl/parser_misc_test.go covering parsePattern dir-mode with
    args, unknown pattern field, non-ident in pattern, top-level
    binary / sources / normalize_crlf / trim_trailing_ws / bare-int
    memory_limit, parseBool invalid ident and non-ident, matcher
    without an operator, validateBuilds legacy+structured conflict.
  - Add dsl/build_parser_test.go covering every BuildConfig field
    (sources, includes, sanitize, link, extra, platforms, compilers,
    defines), OS overrides on named builds, nested / duplicate OS
    override errors, unknown build / profile / warnings / platform,
    missing = on assign-string and assign-string-list, define(...)
    error cases, and parseToolchainsBlock (duplicate name, missing
    platforms, bad name token, unknown field, unknown compiler class,
    binary and class propagation).
  - Add dsl/lexer_test.go for Token.String, TokenType.String UNKNOWN
    branch, line comments, unterminated string and heredoc, unknown
    escape sequence, escape decoding, unexpected character, every
    K/M/G/KiB/MiB/GiB size suffix, ms/s/m duration suffixes, negative
    integer lexing and float literals.
  - Extend runner/result_test.go with Status.String and
    TestResult.addFailure (both previously 0%).
  - Add .gitea/workflows/go-test.yml running `go vet` and
    `go test -race -coverprofile=coverage.out ./...` on push,
    pull_request and manual dispatch, uploading coverage.out as an
    artifact.

  Coverage: dsl 60.5% -> 85%+, runner 29.0% -> 30.5%.

dsl/build_string_test.go

@@ -0,0 +1,74 @@
+package dsl
+
+import "testing"
+
+func TestBuildProfileString(t *testing.T) {
+	cases := []struct {
+		p    BuildProfile
+		want string
+	}{
+		{ProfileRelease, "release"},
+		{ProfileDebug, "debug"},
+		{ProfileSanitized, "sanitized"},
+		{ProfileUnset, "unset"},
+		{BuildProfile(999), "unset"},
+	}
+	for _, c := range cases {
+		if got := c.p.String(); got != c.want {
+			t.Errorf("BuildProfile(%d).String() = %q, want %q", c.p, got, c.want)
+		}
+	}
+}
+
+func TestWarningLevelString(t *testing.T) {
+	cases := []struct {
+		w    WarningLevel
+		want string
+	}{
+		{WarningsDefault, "default"},
+		{WarningsStrict, "strict"},
+		{WarningsPedantic, "pedantic"},
+		{WarningsUnset, "unset"},
+		{WarningLevel(999), "unset"},
+	}
+	for _, c := range cases {
+		if got := c.w.String(); got != c.want {
+			t.Errorf("WarningLevel(%d).String() = %q, want %q", c.w, got, c.want)
+		}
+	}
+}
+
+func TestMergeFromWrapperAndDefines(t *testing.T) {
+	dst := &BuildConfig{}
+	src := &BuildConfig{
+		Wrapper: "valgrind",
+		Defines: map[string]string{"DEBUG": "1", "VERSION": "2"},
+	}
+	dst.MergeFrom(src)
+	if dst.Wrapper != "valgrind" {
+		t.Errorf("Wrapper = %q, want valgrind", dst.Wrapper)
+	}
+	if dst.Defines["DEBUG"] != "1" || dst.Defines["VERSION"] != "2" {
+		t.Errorf("Defines = %v", dst.Defines)
+	}
+}
+
+func TestMergeFromDefinesIntoExisting(t *testing.T) {
+	dst := &BuildConfig{Defines: map[string]string{"KEEP": "old"}}
+	src := &BuildConfig{Defines: map[string]string{"NEW": "1", "KEEP": "new"}}
+	dst.MergeFrom(src)
+	if dst.Defines["KEEP"] != "new" {
+		t.Errorf("KEEP = %q, want new (overridden)", dst.Defines["KEEP"])
+	}
+	if dst.Defines["NEW"] != "1" {
+		t.Errorf("NEW = %q, want 1", dst.Defines["NEW"])
+	}
+}
+
+func TestMergeFromNilSrc(t *testing.T) {
+	dst := &BuildConfig{Language: "c"}
+	dst.MergeFrom(nil)
+	if dst.Language != "c" {
+		t.Errorf("dst mutated on nil merge: %+v", dst)
+	}
+}