Rename/deprecate into bits to format bits (#14634)

# Description
`into bits` is a bad name because it is not a traditional type cast to a
`bits` type like all the other `into` commands.

Instead it is a pretty printer generating `string` type output. Thus the
correct bucket is `format` and its subcommands.


# User-Facing Changes
`into bits` will raise a `DeprecatedWarning` suggesting the move to
`format bits`
`into bits` can be removed in `0.103.0`

# Tests + Formatting
All tests that relied on `into bits` have been updated to `format bits`

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

@@ -1 +1 @@
-mod into;
+mod format;