Ensure LSP readLoop doesn't block shutdown

[jakebailey]

Sort of pulled out of #991, but I'm hoping this helps people who are seeing their tsgo processes not exit.

The next measure we could take is to watch the parent process (PID is given during init) and exit if it exits.

[Copilot]

Pull Request Overview

This PR prevents the readLoop from blocking process shutdown by running it in a standalone goroutine and tweaks the error check on g.Wait().

• Extract readLoop out of the error group so it’s not tied to the group’s cancellation.
• Spawn readLoop in a fire-and-forget goroutine and suppress its error.
• Refine the g.Wait() error condition to also check ctx.Err().

Comments suppressed due to low confidence (1)

internal/lsp/server.go:201

• Requiring ctx.Err() != nil in the error check may suppress genuine errors from dispatchLoop or writeLoop when the context hasn't been cancelled. Consider reverting to the original condition (err != nil && !errors.Is(err, io.EOF)) to ensure you don’t miss critical failures.

if err := g.Wait(); err != nil && !errors.Is(err, io.EOF) && ctx.Err() != nil {

[jakebailey]

This goroutine can leak if the reader never exits, but I'm trying to handle the case where the process is exiting due to a cancellation cancel via a signal, so, it's hard to do better here without cancelable stdin reads ☹️