Skip JSON serialisation if already JSON (json_verbatim)

[anthonynorth]

Could we optionally skip json serialisation of character vectors that are already json? This is {jsonlite}'s json_verbatim = TRUE option. Example:

my_obj <- list(already_json = structure('{"leave_me_alone":"yes"}', class = "json"))
yyjsonr::write_json_str(my_obj, list(skip_json = TRUE))

Expected output

{"already_json":{"leave_me_alone":"yes"}}

[mmuurr]

+1 for this, as it's the only blocker to me switching much of my code that uses {jsonlite} to {yyjsonr} instead.

I took a brief look at the yyjson docs and think the canonical way to do this is:

1. Parse the "json"-classed string (i.e. length-1 STRSXP) into a new yyjsonr doc (call it *x).
2. Insert x into the recursively-growing parent doc.

It looks like yyjson requires that first parsing step to force validity of the growing structure (prior to serialization), though it smells a bit of inefficiency (if we know a priori that the string is guaranteed to be valid JSON). Nevertheless, if there's general agreement from the maintainers here that this is indeed the appropriate approach, I'm happy to take a stab at a PR to implement this feature.

[mmuurr]

A closer look at the yyjson architecture suggests that one might be able to skip the parsing step (mentioned above) and set an element's value to a "raw" *char.