chore: deprecate `Lean.Data.RBMap` and `Lean.Data.RBTree`

This PR deprecates the `Lean.RBMap` and `Lean.RBTree` containers in favour of
`Std.TreeMap` and `Std.TreeSet`, which offer a more complete and consistent API.
Nothing in the Lean repository uses these types any longer, and downstream code
should migrate to the `Std` containers.

The modules are marked with `deprecated_module`, so any file that directly
imports `Lean.Data.RBMap` or `Lean.Data.RBTree` now receives a deprecation
warning. The few internal importers (the `Lean.Data` re-export, `RBTree`'s
import of `RBMap`, and the two compile tests that exercise the API on purpose)
carry a `-- deprecated_module: ignore` annotation. This mirrors the
corresponding deprecation of `Batteries.RBMap` in
https://github.com/leanprover-community/batteries/pull/1792.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>