Problem:
`TSNode:id()` returns the underlying c pointer as a string, which may include
NUL bytes. In PUC Lua, `('%s'):format('\0a\0')` returns `''` and not `'\0a\0'`
(i.e. treats the string as a c-string (which terminates at the NUL byte)).
This resulted in two different nodes being able to have the same id.
Solution:
Use concatenation `..` instead of `string.format()`.
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