Proposal: Drop outPathLen

[mtlynch]

In the C implementation, we have to track out_path_len separately from out_path because the C implementation uses a fixed-length buffer to store out_path and uses out_path_len to indicate which bytes are valid.

In JavaScript, there's no reason to store out_path (outPath) as a fixed-width buffer because JavaScript tracks the length of a Uint8Array for us, so outPathLen becomes unnecessary.

Getting rid of outPathLen simplifies the JavaScript semantics because now the caller can just check outPath and know that the entire value is valid.

I implemented this change, and you can see how it looks in my repo on top of the tests in #11:

https://github.com/mtlynch/meshcore.js/compare/test-frame-parse...mtlynch:meshcore.js:no-outpath-len?expand=1