refactor: Update AFTN message parsing logic

The code changes in `aviation_parser_test.go` update the AFTN message parsing logic. The `ParseHeader` function now returns an additional error value, allowing for better error handling. The tests have been updated to reflect this change, ensuring that the parsing function handles errors correctly. This refactor improves the reliability and maintainability of the AFTN message parsing functionality.

internal/parsers/aviation_parser_test.go

@@ -125,7 +125,7 @@ NNNN
 	})
 	Describe("ParseBody", func() {
 		Context("with ARR body", func() {
-			parser := DefaultBodyParser()
+			parser := NewBodyParser()
 			It("should parse the body (ARR-AB123-SSR1234-KJFK-KLAX) correctly", func() {
 				body := "(ARR-AB123-SSR1234-KJFK-KLAX)"
 				parsedBody, err := parser.Parse(body)
@@ -143,7 +143,7 @@ NNNN
 		})
 
 		Context("with DEP body", func() {
-			parser := DefaultBodyParser()
+			parser := NewBodyParser()
 			It("should parse the body (DEP-AB123-SSR1234-KJFK-1500-KLAX) correctly", func() {
 				body := "(DEP-AB123-SSR1234-KJFK-1500-KLAX)"
 				parsedBody, err := parser.Parse(body)
@@ -161,7 +161,7 @@ NNNN
 		})
 
 		Context("with FPL body", func() {
-			parser := DefaultBodyParser()
+			parser := NewBodyParser()
 			It("should parse the body correctly", func() {
 				body := `(FPL-CCA1532-IS
 -A332/H