Cannot create a string longer than 0x1fffffe8 characters

Nobody has claimed this yet.

So... it would seem that the code tries to slurp the whole file into memory in one go, and convert it to one big string. That's not a good idea....

```
Error: Cannot create a string longer than 0x1fffffe8 characters
at Buffer.toString (node:buffer:784:17)
at convert (C:\Users\chris\GITW\nsldist\client\node_modules\csv2geojson\csv2geojson:23:34)
at ConcatStream. (C:\Users\chris\GITW\nsldist\client\node_modules\concat-stream\index.js:36:43)
at ConcatStream.emit (node:events:402:35)
at finishMaybe (C:\Users\chris\GITW\nsldist\client\node_modules\readable-stream\lib\_stream_writable.js:475:14)
at endWritable (C:\Users\chris\GITW\nsldist\client\node_modules\readable-stream\lib\_stream_writable.js:485:3)
at ConcatStream.Writable.end (C:\Users\chris\GITW\nsldist\client\node_modules\readable-stream\lib\_stream_writable.js:455:41)
at ReadStream.onend (node:internal/streams/readable:693:10)
at Object.onceWrapper (node:events:509:28)
at ReadStream.emit (node:events:390:28) {
code: 'ERR_STRING_TOO_LONG'
}```

Start at the convert call shown at node_modules/csv2geojson:23:34 and inspect how concat-stream supplies the file contents. Reproduce the failure with an input exceeding Node's string limit; done means oversized CSV files no longer fail with ERR_STRING_TOO_LONG.

Written by the indexing model from the issue text.