Neocaml 0.6: Opam, Dune, and More

Neocaml 0.6 is a significant release for the Emacs OCaml package, adding Tree-sitter-based major modes for Opam and Dune files. The new neocaml-opam-mode provides font-lock, indentation, Imenu navigation, and a flymake backend running opam lint for inline diagnostics. neocaml-dune-mode handles dune, dune-project, and dune-workspace files with syntax highlighting, indentation, and stanza navigation. A new neocaml-dune-interaction-mode minor mode adds keybindings for common Dune commands (build, test, clean, format, run) with watch mode support and utop REPL integration. All new modes are isolated from the core OCaml modes and optional. Known rough edges include immature upstream Tree-sitter grammars for Opam and Dune, with the author actively contributing fixes upstream.