fix: Minor issues #12 and #13 - ASCII mode and performance optimization

This commit addresses the remaining Minor issues from PR #94 code review:

Minor #12: Unicode Symbol Compatibility
- Added CODEAGENT_ASCII_MODE environment variable support
- When set to "true", uses ASCII symbols: PASS/WARN/FAIL
- Default behavior (unset or "false"): Unicode symbols ✓/⚠️/✗
- Updated help text to document the environment variable
- Added tests for both ASCII and Unicode modes

Implementation:
- executor.go:514: New getStatusSymbols() function
- executor.go:531: Dynamic symbol selection in generateFinalOutputWithMode
- main.go:34: useASCIIMode variable declaration
- main.go:495: Environment variable documentation in help
- executor_concurrent_test.go:292: Tests for ASCII mode
- main_integration_test.go:89: Parser updated for both symbol formats

Minor #13: Performance Optimization - Reduce Repeated String Operations
- Optimized Message parsing to split only once per task result
- Added *FromLines() variants of all extractor functions
- Original extract*() functions now wrap *FromLines() for compatibility
- Reduces memory allocations and CPU usage in parallel execution

Implementation:
- utils.go:300: extractCoverageFromLines()
- utils.go:390: extractFilesChangedFromLines()
- utils.go:455: extractTestResultsFromLines()
- utils.go:551: extractKeyOutputFromLines()
- main.go:255: Single split with reuse: lines := strings.Split(...)

Backward Compatibility:
- All original extract*() functions preserved
- Tests updated to handle both symbol formats
- No breaking changes to public API

Test Results:
- All tests pass: go test ./... (40.164s)
- ASCII mode verified: PASS/WARN/FAIL symbols display correctly
- Unicode mode verified: ✓/⚠️/✗ symbols remain default
- Performance: Single split per Message instead of 4+

Usage Examples:
  # Unicode mode (default)
  ./codeagent-wrapper --parallel < tasks.txt

  # ASCII mode (for terminals without Unicode support)
  CODEAGENT_ASCII_MODE=true ./codeagent-wrapper --parallel < tasks.txt

Benefits:
- Improved terminal compatibility across different environments
- Reduced memory allocations in parallel execution
- Better performance for large-scale parallel tasks
- User choice between Unicode aesthetics and ASCII compatibility

Related: #94

Generated with SWE-Agent.ai

Co-Authored-By: SWE-Agent.ai <noreply@swe-agent.ai>

codeagent-wrapper/executor_concurrent_test.go

@@ -289,6 +289,45 @@ func TestExecutorHelperCoverage(t *testing.T) {
 		}
 	})
 
+	t.Run("generateFinalOutputASCIIMode", func(t *testing.T) {
+		t.Setenv("CODEAGENT_ASCII_MODE", "true")
+
+		results := []TaskResult{
+			{TaskID: "ok", ExitCode: 0, Coverage: "92%", CoverageNum: 92, CoverageTarget: 90, KeyOutput: "done"},
+			{TaskID: "warn", ExitCode: 0, Coverage: "80%", CoverageNum: 80, CoverageTarget: 90, KeyOutput: "did"},
+			{TaskID: "bad", ExitCode: 2, Error: "boom"},
+		}
+		out := generateFinalOutput(results)
+
+		for _, sym := range []string{"PASS", "WARN", "FAIL"} {
+			if !strings.Contains(out, sym) {
+				t.Fatalf("ASCII mode should include %q, got: %s", sym, out)
+			}
+		}
+		for _, sym := range []string{"✓", "⚠️", "✗"} {
+			if strings.Contains(out, sym) {
+				t.Fatalf("ASCII mode should not include %q, got: %s", sym, out)
+			}
+		}
+	})
+
+	t.Run("generateFinalOutputUnicodeMode", func(t *testing.T) {
+		t.Setenv("CODEAGENT_ASCII_MODE", "false")
+
+		results := []TaskResult{
+			{TaskID: "ok", ExitCode: 0, Coverage: "92%", CoverageNum: 92, CoverageTarget: 90, KeyOutput: "done"},
+			{TaskID: "warn", ExitCode: 0, Coverage: "80%", CoverageNum: 80, CoverageTarget: 90, KeyOutput: "did"},
+			{TaskID: "bad", ExitCode: 2, Error: "boom"},
+		}
+		out := generateFinalOutput(results)
+
+		for _, sym := range []string{"✓", "⚠️", "✗"} {
+			if !strings.Contains(out, sym) {
+				t.Fatalf("Unicode mode should include %q, got: %s", sym, out)
+			}
+		}
+	})
+
 	t.Run("executeConcurrentWrapper", func(t *testing.T) {
 		orig := runCodexTaskFn
 		defer func() { runCodexTaskFn = orig }()