`cabal run` should send info logging to stderr not stdout

`cabal run` prints stuff like "up to date" to stdout. So running an executable and `cabal run` an executable give different output to stdout, which is no good when the executable is producing output for e.g. machine consumption. We should do our info logging to stderr.

Start by tracing how `cabal run` emits its informational messages and handles stdout versus stderr. Verify that the executable's stdout remains clean for machine consumption while messages such as "up to date" are sent to stderr.

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