chore: bump dependencies

[vihu]

Summary

Upgrade nvim-oxi from 0.4.2 to 0.6.0 and tokio-tungstenite from 0.21.0 to 0.28.0, addressing all breaking API changes and removing dead code discovered during the migration.

Changes

• Upgrade nvim-oxi from 0.4.2 to 0.6.0 with neovim feature flag 0.9 to 0.11
• Upgrade tokio-tungstenite from 0.21.0 to 0.28.0
• Replace direct mlua dependency with nvim-oxi re-export (nvim_oxi::mlua)
• Migrate from #[nvim_oxi::module] to #[nvim_oxi::plugin] attribute
• Update mlua imports to use nvim_oxi::mlua path
• Remove lifetime parameter from IntoLua trait implementations
• Remove lifetime parameter from LuaFunction types
• Update LuaTable.get() and LuaFunction.call() call sites for new signatures
• Add explicit type annotations to Function::from_fn() calls
• Update tungstenite Message::Text to use Utf8Bytes instead of String
• Remove unused struct fields: extra_headers, task_handle
• Remove unused enum variants: Forceful, DisconnectionError, ClientConnectionError
• Remove unused TryFromStr trait
• Remove unused get() method from registry module
• Rename enum variants for conciseness (e.g., ConnectionError to Connection)
• Fix typo: client_temrination_error to client_termination_error
• Apply minor formatting fixes to CI workflow