@Test void annotation_sizeInBytes() {
    AnnotationField field = new AnnotationField(1 << 3 | WIRETYPE_LENGTH_DELIMITED);
    assertThat(field.sizeInBytes(Annotation.create(1L, "12345678")))
      .isEqualTo(0
        + 1 /* tag of timestamp field */ + 8 /* 8 byte number */
        + 1 /* tag of value field */ + 1 /* len */ + 8 // 12345678
        + 1 /* tag of annotation field */ + 1 /* len */
      );
  }
A map entry is an embedded messages: one for field the key and one for the value
zipkin/src/test/java/zipkin2/internal/Proto3ZipkinFieldsTest.java