@Test void field_key_fieldOneLengthDelimited() {
    Field field = new Field(1 << 3 | WIRETYPE_LENGTH_DELIMITED);
    assertThat(field.key)
      .isEqualTo(0b00001010) // (field_number << 3) | wire_type = 1 << 3 | 2
      .isEqualTo(10); // for sanity of those looking at debugger, 4th bit + 2nd bit = 10
    assertThat(field.fieldNumber)
      .isEqualTo(1);
    assertThat(field.wireType)
      .isEqualTo(WIRETYPE_LENGTH_DELIMITED);
  }
Shows we can reliably look at a byte zero to tell if we are decoding proto3 repeated fields.
zipkin/src/test/java/zipkin2/internal/Proto3FieldsTest.java