refactor: move to tower_lsp

[juleswritescode]

• refactor the pg_lsp crate so it implements the tower_lsp LanguageServer trait
• this makes it such that we use tokio for the server :)
• use tower_lsp's rexported lsp_types instead of the plain crate
• remove the DebouncerThread, use a simple debouncer that uses tokio's channels instead
• add tracing to the pg_lsp crate, which will write logs into a pglsp.log file
• refactor the pg_lsp crate such that the "business logic" (database + ide) is separate from the server

What this doesn't do:

• I can't guarantee that all the LSP-requests work as expected – but we'll have tests soon :)
• logging isn't configurable yet; ideally, we would configure the log levels via env-vars/lsp-config and use rolling log files (like biomejs does)