move common tools from nu-command to nu-cmd-base (#9455)

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
```

crates/nu-command/src/strings/encode_decode/base64.rs

@@ -1,8 +1,8 @@
-use crate::input_handler::{operate as general_operate, CmdArgument};
 use base64::{
     alphabet, engine::general_purpose::NO_PAD, engine::general_purpose::PAD,
     engine::GeneralPurpose, Engine,
 };
+use nu_cmd_base::input_handler::{operate as general_operate, CmdArgument};
 use nu_engine::CallExt;
 use nu_protocol::ast::{Call, CellPath};
 use nu_protocol::engine::{EngineState, Stack};

crates/nu-command/src/strings/encode_decode/hex.rs

@@ -1,4 +1,4 @@
-use crate::input_handler::{operate as general_operate, CmdArgument};
+use nu_cmd_base::input_handler::{operate as general_operate, CmdArgument};
 use nu_engine::CallExt;
 use nu_protocol::ast::{Call, CellPath};
 use nu_protocol::engine::{EngineState, Stack};