read write cycle testing

[ix0rai]

hopefully the last pr of the 1.2 cycle. adds extensive testing for read/write cycle to ensure no data is lost during reading or writing fixes #19

contains one API addition: MetadataContainer#metadata()

         /**
     * @return a map of all metadata attached to this node
     */
    Map<MetadataType<?, ?>, Object> metadata();

TODO:

• [x] add tests that simply read the file and compare against a string, to ensure formatting is proper - decided against doing this
• [x] expand read/write tests

notes:

• diff is huge because it's 2024 and licenses need updating
• shouldn't change functionality of anything. I haven't found any issues in writing these tests (so far)