* interp: fix creation of binary composite types
Use direct assignment instead of reflect.Value Set method to
initialize a binary composite type, as for non binary types.
It ensures that a new reflect.Value is stored in the frame
instead of modifying a possibly existing one, which can defeat
the purpose of initializing variables in a body loop.
While there, remove the need to have and use a mutex on types.
Fixes#1381.
* review: rework a bit the test
Co-authored-by: mpl <mathieu.lonjaret@gmail.com>
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