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%.

runner/result_test.go

@@ -1,6 +1,44 @@
 package runner
 
-import "testing"
+import (
+	"strings"
+	"testing"
+)
+
+func TestStatusString(t *testing.T) {
+	cases := []struct {
+		s    Status
+		want string
+	}{
+		{StatusPass, "PASS"},
+		{StatusFail, "FAIL"},
+		{StatusTLE, "TLE"},
+		{StatusMLE, "MLE"},
+		{StatusBuildError, "BUILD_ERROR"},
+		{StatusRuntimeError, "RE"},
+		{Status(999), "UNKNOWN"},
+	}
+	for _, c := range cases {
+		if got := c.s.String(); got != c.want {
+			t.Errorf("Status(%d).String() = %q, want %q", c.s, got, c.want)
+		}
+	}
+}
+
+func TestAddFailureAppends(t *testing.T) {
+	r := &TestResult{}
+	r.addFailure("first %s", "msg")
+	r.addFailure("second %d", 2)
+	if len(r.Failures) != 2 {
+		t.Fatalf("Failures len = %d, want 2", len(r.Failures))
+	}
+	if r.Failures[0] != "first msg" {
+		t.Errorf("Failures[0] = %q", r.Failures[0])
+	}
+	if !strings.Contains(r.Failures[1], "second 2") {
+		t.Errorf("Failures[1] = %q", r.Failures[1])
+	}
+}
 
 func TestAggregateScoreEmpty(t *testing.T) {
 	r := &SuiteResult{}