fix(lsp): ensure child process terminates when parent exits

[tartarughina]

Address #41

Implemented a robust cleanup strategy for the spawned LSP process to prevent zombie processes:

• Added detached: false to the spawn configuration
• Implemented a cleanup function that attempts a graceful SIGTERM, followed by a forced SIGKILL after 1s if needed
• Added a listener on stdin end for graceful shutdown
• Added a watchdog interval to monitor the parent process (PPID); if the parent dies ungracefully, the LSP process will now self-terminate.

[tartarughina]

I've conducted the following testing:

• Connected to a remote machine via SSH and on TMUX started bottom (btm) to track system resources
• Connected to the same machine with Zed Remote
• From TMUX session, verified that Zed spawned the node (proxy) and java (jdtls) processes and logged their PIDs
• Closed Zed -> node and java processes closed as expected handling the end from stdin
• Let SSH connection for Zed Remote break -> zombie node and java processes terminated after timeout as PPID no longer present

I've run a similar test on Mac, it appears that the most effective measure here was coming from the watchdog.
I'm unable to test on Windows, so before merging the changes it would be good to have someone trying this out over there.

[playdohface]

It looks good. I don't have Windows running to actually test this, and the whole process-business is very OS-specific so let's make sure we have someone run this on Windows before making it part of a release

[tartarughina]

@playdohface I've added specific Windows handling to the cleanup function, as well as in the watchdog. I've created a Windows VM and I'm going to run some tests over there. If everything works as expected I'll proceed to merge the changes.