Msgpack commands (#12664)

# Description

I thought about bringing `nu_plugin_msgpack` in, but that is MPL with a
clause that prevents other licenses, so rather than adapt that code I
decided to take a crack at just doing it straight from `rmp` to `Value`
without any `rmpv` in the middle. It seems like it's probably faster,
though I can't say for sure how much with the plugin overhead.

@IanManske I started on a `Read` implementation for `RawStream` but just
specialized to `from msgpack` here, but I'm thinking after release maybe
we can polish it up and make it a real one. It works!

# User-Facing Changes
New commands:

- `from msgpack`
- `from msgpackz`
- `to msgpack`
- `to msgpackz`

# Tests + Formatting
Pretty thorough tests added for the format deserialization, with a
roundtrip for serialization. Some example tests too for both `from
msgpack` and `to msgpack`.

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`


# After Submitting
- [ ] update release notes

crates/nu-command/src/default_context.rs

@@ -260,6 +260,8 @@ pub fn add_shell_command_context(mut engine_state: EngineState) -> EngineState {
             From,
             FromCsv,
             FromJson,
+            FromMsgpack,
+            FromMsgpackz,
             FromNuon,
             FromOds,
             FromSsv,
@@ -273,6 +275,8 @@ pub fn add_shell_command_context(mut engine_state: EngineState) -> EngineState {
             ToCsv,
             ToJson,
             ToMd,
+            ToMsgpack,
+            ToMsgpackz,
             ToNuon,
             ToText,
             ToToml,