fix: address code quality issues from golangci-lint

- Fix error handling in test files by explicitly ignoring error returns
- Remove trailing punctuation from error message in rpn_parse.go

Test file changes:
- cli_test.go: Use _ = os.Remove() in Cleanup function
- concurrent_test.go: Use _, _ = runRPN() in concurrent goroutines

Code change:
- rpn_parse.go: Changed error message to end with 'colon' instead of ':'

3 files changed, 7 insertions, 4 deletions

diff --git a/cmd/gt/cli_test.go b/cmd/gt/cli_test.go
index e725de9..46d9e82 100644
--- a/cmd/gt/cli_test.go
+++ b/cmd/gt/cli_test.go
@@ -27,7 +27,8 @@ func buildBinary(t *testing.T) string {
 	}
 	
 	t.Cleanup(func() {
-		os.Remove("/tmp/gt-test")
+		// Explicitly ignore error return from os.Remove during cleanup
+		_ = os.Remove("/tmp/gt-test")
 	})
 	
 	return "/tmp/gt-test"
diff --git a/internal/repl/concurrent_test.go b/internal/repl/concurrent_test.go
index 14c82ef..d07b9ce 100644
--- a/internal/repl/concurrent_test.go
+++ b/internal/repl/concurrent_test.go
@@ -25,7 +25,8 @@ func TestConcurrentRPN(t *testing.T) {
 		wg.Add(1)
 		go func(id int) {
 			defer wg.Done()
-			runRPN("3 4 +")
+			// Ignore error return as the expression "3 4 +" should always succeed
+			_, _ = runRPN("3 4 +")
 		}(i)
 	}
 	wg.Wait()
@@ -55,7 +56,8 @@ func TestConcurrentExecutorAndRPN(t *testing.T) {
 		}(i)
 		go func(id int) {
 			defer wg.Done()
-			runRPN("3 4 +")
+			// Ignore error return as the expression "3 4 +" should always succeed
+			_, _ = runRPN("3 4 +")
 		}(i)
 	}
 	wg.Wait()
diff --git a/internal/rpn/rpn_parse.go b/internal/rpn/rpn_parse.go
index 48abb15..bf9a613 100644
--- a/internal/rpn/rpn_parse.go
+++ b/internal/rpn/rpn_parse.go
@@ -445,7 +445,7 @@ func (r *RPN) handleOperator(stack *Stack, token string, tokenIndex int) (string
 	if len(token) > 0 && token[0] == ':' {
 		symbolName := token[1:] // Remove the leading :
 		if symbolName == "" {
-			return "", fmt.Errorf("symbol name cannot be empty after :")
+			return "", fmt.Errorf("symbol name cannot be empty after colon")
 		}
 		// Only push as symbol if the remaining part is a valid identifier
 		// This prevents := and =: from being treated as : followed by = operator