Improve the error message for a plugin version mismatch (#12122)

# Description

Previously, the plugin itself would also print error messages about
mismatched versions, and there could be many of them while parsing a
`register` command which would be hard to follow. This removes that
behavior so that the error message is easier to read, and also makes the
error message on the engine side mention the plugin name so that it's
easier to tell which plugin needs to be updated.

The python plugin has also been modified to make testing this behavior
easier. Just change `NUSHELL_VERSION` in the script file to something
incompatible.

# User-Facing Changes
- Better error message

# Tests + Formatting
- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

crates/nu_plugin_python/nu_plugin_python_example.py

@@ -27,6 +27,9 @@ import sys
 import json
 
 
+NUSHELL_VERSION = "0.91.1"
+
+
 def signatures():
     """
     Multiple signatures can be sent to Nushell. Each signature will be registered
@@ -175,7 +178,7 @@ def tell_nushell_hello():
     hello = {
         "Hello": {
             "protocol": "nu-plugin", # always this value
-            "version": "0.90.2",
+            "version": NUSHELL_VERSION,
             "features": []
         }
     }
@@ -216,7 +219,10 @@ def write_error(id, msg, span=None):
 
 def handle_input(input):
     if "Hello" in input:
-        return
+        if input["Hello"]["version"] != NUSHELL_VERSION:
+            exit(1)
+        else:
+            return
     elif input == "Goodbye":
         return
     elif "Call" in input: