Fix incorrect SNBT string and key quoting

[Esper89]

SNBT strings and keys that start with a number (or that start or end with whitespace) need to be quoted to preserve their value and type. Currently, if you run this library's SNBT output back into it's own SNBT parser:

• Strings like "0" are converted to integers.
• Strings like "1.2.3" cause an error.
• Strings like " foo " have their leading and trailing whitespace stripped.
• Keys like "0" or "1.2.3" cause an error.
• Keys like " foo " have their leading and trailing whitespace stripped.

I encountered this problem while formatting a level.dat file as SNBT and parsing the output—version strings like "1.19.4" caused parse errors, and the values of game rules like randomTickSpeed: "3" were incorrectly converted from strings to integers.

This PR fixes these issues.

[Cassy343]

Thanks for pointing out these issues and fixing them. Could you add some tests consisting of the cases you outlined in your description?

[Esper89]

I've added the test cases.

[Cassy343]

Thanks, looks good to me.

[Cassy343]

Released in version 0.2.8