Make into bits produce bitstring stream (#13310)

# Description

Fix `into bits` to have consistent behavior when passed a byte stream.

# User-Facing Changes

Previously, it was returning a binary on stream, even though its
input/output types don't describe this possibility. We don't need this
since we have `into binary` anyway.

# Tests + Formatting
Tests added

crates/nu-cmd-extra/tests/commands/mod.rs

@@ -1 +1,2 @@
+mod bits;
 mod bytes;