Add keyword-driven completions for BLOCK_LIST and ADDR_LIST in the LSP server.
- While typing a prefix of these keywords the server returns the keyword(s)
as incomplete snippet suggestions that trigger a re-request.
- Once the keyword is typed the server replaces it with a full list of the
corresponding loaded block templates or addresses (quoted), and sets each
item's filter_text to include the keyword so further typing narrows results.
- Integrate this flow into on_completion and factor the symbol-list logic
into a helper that returns either incomplete keyword suggestions or the
completed symbol list.
Also implement NxFormatter.format_comment to ensure a single space after a
leading '#' for comments that don't already start with whitespace, while
leaving sequences of '#' (separators), shebangs, and already-spaced comments
unchanged. This affects both standalone and inline comments.
Add/rename tests to cover the new completions and comment-spacing behavior.
Christoph