* Add test for passing binary data through externals
This change adds an ignored test to confirm that binary data is passed
correctly between externals to be enabled in a later commit along with
the fix.
To assist in platform agnostic testing of binary data a couple of
additional testbins were added to allow testing on `Value::Binary` inside
`ExternalStream`.
* Support binary data to stdin of run-external
Prior to this change, any pipeline producing binary data (not detected
as string) then feed into an external would be ignored due to
run-external only supporting `Value::String` on stdin.
This change adds binary stdin support for externals allowing something
like this for example:
〉^cat /dev/urandom | ^head -c 1MiB | ^pv -b | ignore
1.00MiB
This would previously output `0.00 B [0.00 B/s]` due to the data not
being pushed to stdin at each stage.