Respect output = "raw" in oa_fetch() when result is returned early

[yjunechoe]

In oa_fetch(), there's a clause to return res (the single initial query we do at the start to compute on metadata for stuff like # of pages to expect) early when the meta field is empty (i.e., simple "direct" queries):

openalexR/R/oa_fetch.R

Lines 340 to 347 in 42f4d16

	if (!is.null(res$meta)) {
	## return only item counting
	if (count_only) {
	return(res$meta)
	}
	} else {
	return(res)
	}

At this point of early return, res is always the parsed json, so it was not respecting output = "raw" in cases like oa_fetch(identifier = "W4396214724", output = "raw") which triggers that early return.

The PR makes it so that this initial res can stay either parsed or unparsed, so that it can be returned unparsed if user specifies output = "raw". Since we do need the parsed metadata info, that's now tracked in res_meta. The roundabout way of doing this in the code is to ensure that we only request once and parse as needed.

[trangdata]

LGTM! Thank you June! 🎉