Metadata type mismatch

If I put a number into a clip's metadata, normally it is fine, but if the number is too big, then I get `True` back instead, which is not right.
```
import opentimelineio as otio
c = otio.schema.Clip()
c.metadata["test"]={"foo":9999}
print(c.metadata)
c.metadata["test"]={"foo":99999999999999999999999999999999}
print(c.metadata)

OUTPUT:
{'test': {'foo': 9999}}
{'test': {'foo': True}}
```

Start by running the Python reproduction using c.metadata and compare the results for 9999 and the oversized integer. Trace the metadata assignment and numeric conversion path; done means oversized integer values retain an appropriate numeric value instead of becoming True.

Written by the indexing model from the issue text.