Turn on rust-analyzer's inferred-type hints

[thomasjm]

From plans/inlay-hints-and-notebook-suffixes.md. Stacked on #115 because both regenerate OPTIONS.md; merge that one first.

Issue 1. rust-analyzer ships inlayHints.typeHints.enable off and expects the editor to turn it on, which we don't, so it answers the request with no hints. Now kernels.rust.lsp.rust-analyzer.typeHints, defaulting to true. Checked against a real cargo project: off gives [], on gives : i32 and : String. Left parameterHints and chainingHints alone.

Issue 2 is wrong and isn't here. The plan asks for a notebook_suffix on rust-analyzer and clangd. Doing that breaks both languages' notebooks.

Every notebook proxy — rnls, hnls, cnls, gnls — decides whether a document is a notebook by testing whether its URI ends in .ipynb, and then appends its own extension. Give clangd notebook_suffix = ".cpp" and the document arrives as main.ipynb.cpp, isNotebook is false, cnls skips the declaration sifter and the __notebook_exec wrapping entirely, and cell statements go to clangd raw. I confirmed it: documentSymbol on int x = 1; x = 2; returns [] as probe.ipynb (notebook path active) and two x symbols as probe.ipynb.cpp (treated as an ordinary file). Same for rust — as .ipynb a cell formats, as .ipynb.rs nothing comes back.

So the empty notebook_suffix on rust-analyzer, clangd, gopls and haskell-language-server is load-bearing, not an oversight. It's exactly the four servers that sit behind a proxy; the ones with a real suffix (jedi, tinymist, solargraph, …) have none.

What the plan actually diagnosed for clangd — requests failing with "non-added document" — has the same cause as the Rust formatting bug: the proxy doesn't rewrite the URI for those methods. The fix belongs in the proxies:

• rust-notebook-language-server: formatting, onTypeFormatting, inlayHint — Handle textDocument/formatting, onTypeFormatting and inlayHint rust-notebook-language-server#2
• haskell-notebook-language-server: inlayHint — Handle textDocument/inlayHint haskell-notebook-language-server#2
• cpp-notebook-language-server and go-notebook-language-server: same three methods missing, not yet done