feat(lsp): support completion item resolve to show .def previews

Enable completion item resolution so selecting a completion can populate
documentation with a preview of the corresponding .def declaration.

- Turn on resolve_provider in the completion options.
- Implement on_completion_resolve to attach Markdown documentation
  computed by def_hover_markdown when the completion item's data
  contains a ("def" -> [kind, name]) payload.
- Include that "def" payload when generating def-related completion items.
- Add tests that verify block-template and address-list items resolve to
  Markdown previews.

Before: def-related completion items had no documentation on resolve.
After: selecting such items will return a Markdown preview of the .def entry.

server/tests/python_tests/test_def_symbols.py

@@ -227,6 +227,25 @@ def test_block_list_shows_all_templates_quoted(tmp_path, monkeypatch):
     assert all(item.filter_text.startswith("BLOCK_LIST") for item in items)
 
 
+def test_block_list_item_resolves_to_template_preview(tmp_path, monkeypatch):
+    server, _ = _project(tmp_path, monkeypatch)
+    items = _complete(server, tmp_path, "set a 1\n    BLOCK_LIST")
+    assert all(item.documentation is None for item in items)
+    item = next(item for item in items if item.label == "steady_rest")
+    resolved = lsp_server.on_completion_resolve(item)
+    assert resolved.documentation.kind == lsp.MarkupKind.Markdown
+    assert "**Block template** `steady_rest`" in resolved.documentation.value
+    assert "Text[M60]" in resolved.documentation.value
+
+
+def test_address_list_item_resolves_to_address_table(tmp_path, monkeypatch):
+    server, _ = _project(tmp_path, monkeypatch)
+    items = _complete(server, tmp_path, "set a 1\n    ADDR_LIST")
+    item = next(item for item in items if item.label == "SPOS")
+    resolved = lsp_server.on_completion_resolve(item)
+    assert "| Format | `Coordinate` |" in resolved.documentation.value
+
+
 def test_block_list_ignores_variables_and_other_words(tmp_path, monkeypatch):
     server, _ = _project(tmp_path, monkeypatch)
     for source in ("set x $BLOCK_LIST", "set x MY_BLOCK_LIST", "set x steady"):