related to
- https://github.com/nushell/nushell/pull/9404
# Description
to support our cratification effort and moving non-1.0 commands outside
of the main focus, this PR
- creates a new `nu-cmd-base` crate to hold the common structs, traits
and functions used by all command-related crates
- to start the transition, moves the `input_handler` module from
`nu-command` to `nu-cmd-base`
# User-Facing Changes
```
$nothing
```
# Tests + Formatting
- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- ⚫ `toolkit test`
- ⚫ `toolkit test stdlib`
# After Submitting
```
$nothing
```
