[ty] Add a warning about pre-release status to the CLI (#17983)

Summary
--

This was suggested on Discord, I hope this is roughly what we had in
mind. I took the message from the ty README, but I'm more than happy to
update it. Otherwise I just tried to mimic the appearance of the `ruff
analyze graph` warning (although I'm realizing now the whole text is
bold for ruff).

Test Plan
--

New warnings in the CLI tests. I thought this might be undesirable but
it looks like uv did the same thing
(https://github.com/astral-sh/uv/pull/6166).


![image](https://github.com/user-attachments/assets/e5e56a49-02ab-4c5f-9c38-716e4008d6e6)

crates/ty/src/lib.rs

@@ -62,6 +62,11 @@ fn run_check(args: CheckCommand) -> anyhow::Result<ExitStatus> {
     countme::enable(verbosity.is_trace());
     let _guard = setup_tracing(verbosity)?;
 
+    tracing::warn!(
+        "ty is pre-release software and not ready for production use. \
+            Expect to encounter bugs, missing features, and fatal errors.",
+    );
+
     tracing::debug!("Version: {}", version::version());
 
     // The base path to which all CLI arguments are relative to.