Make WaveAsset data available to RNBO node earlier

[jinpavg]

As of commit 11c13b82a11233dec9311a48134ce2c581dac572, we are loading WaveAssetDataRef on construction if available rather than later in Execute()

In general, getting RNBO WaveAsset data takes some time -- how early can it be available to the RNBO node?

Is there a way to make a sample RNBO needs available sometime before the source is built?

[jinpavg]

this is related to #29, which concerns datarefs that come over from our RNBO export

[jinpavg]

Just as a note -- even after the change described above, the loading of the data into the RNBO node will still be async, so we can't necessarily know when it will be available. We'll be noting this in the documentation.