feat: support streaming for command File arguments

[phi-bre]

Alternative to #15978 that also supports streaming of files with the lazy file implementation we already have.

But maybe this was already considered and rejected @Rich-Harris? The only negative impact I can think of is that its now a binary format and not human readable, but I already can't make sense of devalue's output personally.

TODO:

• Consider adding Blob support too!
• Add tests (especially: ensure that nested file support isn't accidentally removed from the binary format in the future, as that is the only difference between forms and commands at the moment)

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