Determine cost/benefit of optimizing the allocations

[museun]

There are plenty of clone()/Box::new/to_string() calls. They can be removed with a bit of effort.

Running it over a cargo metadata for a large workspace (522.1 KiB on a single line) in release mode results in:

> wc md.json
       1    4231  534587 .\md.json

peak    7.10MiB
real    0.080s
user    0.062s
sys     0.000s

7 MiB isn't terrible but it could be better.

And on a larger file:

> wc big.json
       1   14754 1669588 .\big.json

peak    13.43MiB
real    0.061s
user    0.047s
sys     0.000s