Upstream: comment on ytsaurus#6 and offer this stack to ytsaurus-rust-sdk

[sshaplygin]

Part of #63. Human-gated — this is a decision about the project's relationship to upstream, not a task to be executed quietly.

ytsaurus/ytsaurus#6 asked for a Rust SDK. The answer this repo can give now is a great deal stronger than it would have been six months ago: nine released crates, an RPC proxy client, dynamic tables over two transports behind one interface, CI with a benchmark gate on every pull request, and compatibility documents that name every open gate rather than claiming there are none.

• comment on ytsaurus/ytsaurus#6 with the current state and links to the in-tree compatibility docs
• offer the stack to ytsaurus/ytsaurus-rust-sdk
• decide first what "offer" means — donate, mirror, or stay independent and be listed — because the answer changes the tone of both messages