Add the inlined data as base64 encoded field and try to add a string version if feasible.
Example:
```
λ xl-meta -data xl.meta
{
"8e03504e-1123-4957-b272-7bc53eda0d55": {
"bitrot_valid": true,
"bytes": 58,
"data_base64": "Z29sYW5nLm9yZy94L3N5cyB2MC4xNS4wIC8=",
"data_string": "golang.org/x/sys v0.15.0 /"
}
```
The string will have quotes, newlines escaped to produce valid JSON.
If content isn't valid utf8 or the encoding otherwise fails, only the base64 data will be added.
`-export` can still be used separately to extract the data as files (including bitrot).
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