Allow plugins to report their own version and store it in the registry (#12883)

# Description

This allows plugins to report their version (and potentially other
metadata in the future). The version is shown in `plugin list` and in
`version`.

The metadata is stored in the registry file, and reflects whatever was
retrieved on `plugin add`, not necessarily the running binary. This can
help you to diagnose if there's some kind of mismatch with what you
expect. We could potentially use this functionality to show a warning or
error if a plugin being run does not have the same version as what was
in the cache file, suggesting `plugin add` be run again, but I haven't
done that at this point.

It is optional, and it requires the plugin author to make some code
changes if they want to provide it, since I can't automatically
determine the version of the calling crate or anything tricky like that
to do it.

Example:

```
> plugin list | select name version is_running pid
╭───┬────────────────┬─────────┬────────────┬─────╮
│ # │      name      │ version │ is_running │ pid │
├───┼────────────────┼─────────┼────────────┼─────┤
│ 0 │ example        │ 0.93.1  │ false      │     │
│ 1 │ gstat          │ 0.93.1  │ false      │     │
│ 2 │ inc            │ 0.93.1  │ false      │     │
│ 3 │ python_example │ 0.1.0   │ false      │     │
╰───┴────────────────┴─────────┴────────────┴─────╯
```

cc @maxim-uvarov (he asked for it)

# User-Facing Changes

- `plugin list` gets a `version` column
- `version` shows plugin versions when available
- plugin authors *should* add `fn metadata()` to their `impl Plugin`,
but don't have to

# Tests + Formatting

Tested the low level stuff and also the `plugin list` column.

# After Submitting
- [ ] update plugin guide docs
- [ ] update plugin protocol docs (`Metadata` call & response)
- [ ] update plugin template (`fn metadata()` should be easy)
- [ ] release notes

crates/nu-plugin-engine/src/persistent.rs

@@ -7,7 +7,7 @@ use super::{PluginInterface, PluginSource};
 use nu_plugin_core::CommunicationMode;
 use nu_protocol::{
     engine::{EngineState, Stack},
-    PluginGcConfig, PluginIdentity, RegisteredPlugin, ShellError,
+    PluginGcConfig, PluginIdentity, PluginMetadata, RegisteredPlugin, ShellError,
 };
 use std::{
     collections::HashMap,
@@ -31,6 +31,8 @@ pub struct PersistentPlugin {
 struct MutableState {
     /// Reference to the plugin if running
     running: Option<RunningPlugin>,
+    /// Metadata for the plugin, e.g. version.
+    metadata: Option<PluginMetadata>,
     /// Plugin's preferred communication mode (if known)
     preferred_mode: Option<PreferredCommunicationMode>,
     /// Garbage collector config
@@ -59,6 +61,7 @@ impl PersistentPlugin {
             identity,
             mutable: Mutex::new(MutableState {
                 running: None,
+                metadata: None,
                 preferred_mode: None,
                 gc_config,
             }),
@@ -268,6 +271,16 @@ impl RegisteredPlugin for PersistentPlugin {
         self.stop_internal(true)
     }
 
+    fn metadata(&self) -> Option<PluginMetadata> {
+        self.mutable.lock().ok().and_then(|m| m.metadata.clone())
+    }
+
+    fn set_metadata(&self, metadata: Option<PluginMetadata>) {
+        if let Ok(mut mutable) = self.mutable.lock() {
+            mutable.metadata = metadata;
+        }
+    }
+
     fn set_gc_config(&self, gc_config: &PluginGcConfig) {
         if let Ok(mut mutable) = self.mutable.lock() {
             // Save the new config for future calls