feat(svm): add which subcommand (#137)

```
svm which 0.8.25
/Users/user/Library/Application Support/svm/0.8.25/solc-0.8.25
```

crates/svm-rs/src/bin/svm-bin/main.rs

@@ -16,6 +16,7 @@ mod print;
 mod remove;
 mod r#use;
 mod utils;
+mod which;
 
 /// Solc version manager.
 #[derive(Debug, Parser)]
@@ -28,6 +29,7 @@ enum Svm {
     List(list::ListCmd),
     Install(install::InstallCmd),
     Use(r#use::UseCmd),
+    Which(which::WhichCmd),
     Remove(remove::RemoveCmd),
 }
 
@@ -41,6 +43,7 @@ async fn main() -> anyhow::Result<()> {
         Svm::List(cmd) => cmd.run().await?,
         Svm::Install(cmd) => cmd.run().await?,
         Svm::Use(cmd) => cmd.run().await?,
+        Svm::Which(cmd) => cmd.run()?,
         Svm::Remove(cmd) => cmd.run().await?,
     }
 

crates/svm-rs/src/bin/svm-bin/which.rs

@@ -0,0 +1,22 @@
+use clap::Parser;
+use semver::Version;
+
+/// Display which binary will be run for a given version.
+#[derive(Debug, Parser)]
+pub struct WhichCmd {
+    /// The version to check.
+    version: Version,
+}
+
+impl WhichCmd {
+    pub fn run(self) -> anyhow::Result<()> {
+        let Self { version } = self;
+        let bin = svm::version_binary(&version.to_string());
+        if bin.exists() {
+            println!("{}", bin.display());
+        } else {
+            return Err(anyhow::anyhow!("version {version} not installed"));
+        }
+        Ok(())
+    }
+}