Upgrade bux-lsp to 0.2.0 with a richer lightweight symbol index:
func signatures, typed let/var/const, struct/enum/interface/type/module.
Skip comments and strings while scanning. Hover shows markdown Bux
code fences; definition resolves in-file and across workspace .bux files;
documentSymbol provides outline. Fix responses writing to stdout (stdin
was a broken pipe). didChange refreshes symbols; diagnostics still run
via buxc on open/save.
Introduce fat function pointers (BuxFn {code, env}) so capturing closures
are heap-allocated per value in both bootstrap and selfhost. Expand
Array/Map/Set/String/Test/Result APIs, add proper tuple codegen and
error snippets with multi-char underlines, golden diagnostic tests, and
LSP diagnostics via buxc check.