refactor(lib): keep the actors inside the crate and mark the growing enums

Every release since 14 has been a major, because the actor mailboxes,
the share index's struct and the CLI's command enum were all exhaustive
public API: adding a peer message, a scanned field or a subcommand read
as a breaking change to the library. The actors, dispatcher, peer
plumbing and download store are how the client is built, not what a host
programs against, so they move inside the crate; PeerMessage, SharedFile
and the CLI command enums are non-exhaustive; ConnectionType is
re-exported at the root for the one thing hosts used it for. A one-time
break so that the next additions are not.

soulseek-rs/src/cli.rs

@@ -172,7 +172,11 @@ pub struct Cli {
     pub log_file: Option<PathBuf>,
 }
 
+/// Non-exhaustive: this enum is public through the crate's library target so
+/// the integration tests can reach it, and a new subcommand must not read as a
+/// breaking change of that library.
 #[derive(Subcommand, Debug)]
+#[non_exhaustive]
 pub enum Commands {
     /// Search the network and print matching files
     Search(SearchArgs),
@@ -254,6 +258,7 @@ pub struct DaemonArgs {
 }
 
 #[derive(Subcommand, Debug)]
+#[non_exhaustive]
 pub enum DaemonCommand {
     /// Print the token remote clients authenticate with
     Token,
@@ -266,6 +271,7 @@ pub enum DaemonCommand {
 }
 
 #[derive(Subcommand, Debug)]
+#[non_exhaustive]
 pub enum CompletionsCommand {
     /// Write the completion script where the shell looks for it
     Install(CompletionsArgs),