leanPackages: structural reimagining — own toolchain, lake --packages, Hydra visibility

Give leanPackages its own lean4, independent of pkgs.lean4. Binary-
patch the toolchain so the language server discovers the wrapped lake
despite lake serve deriving LAKE from IO.appPath unconditionally.
Supplant Lake's config trace validation for /nix/store/ dependencies,
deferring cache coherence to Nix.

Migrate Nix-managed dependency injection from package-overrides.json
to lake --packages. Patch Cli to pre-build static library for
downstream executables. Add recurseIntoAttrs for Hydra.

Upstream accepted FetchContent for mimalloc vendoring:
https://github.com/leanprover/lean4/commit/a145b9c11a0fe38fd4c921024a7376c99cc34bd2

pkgs/development/lean-modules/proofwidgets/default.nix

@@ -8,19 +8,18 @@
 }:
 
 let
+  version = "0.0.95";
   src = fetchFromGitHub {
     owner = "leanprover-community";
     repo = "ProofWidgets4";
-    tag = "v0.0.87";
-    hash = "sha256-qXEqNfwUBPnxAtLRkBZTBFhrM4JYl43gLo/PM6HOG7o=";
+    tag = "v${version}";
+    hash = "sha256-LETljr+QEU6CxprR3pB4hUzhgCD8PrIuiPOgTIdhHVM=";
   };
 in
 
 buildLakePackage {
   pname = "lean4-proofwidgets";
-  version = "0.0.87";
-
-  inherit src;
+  inherit version src;
 
   leanPackageName = "proofwidgets";
 
@@ -38,7 +37,7 @@ buildLakePackage {
     name = "lean4-proofwidgets-npm-deps";
     inherit src;
     sourceRoot = "source/widget";
-    hash = "sha256-CzBRrreOSytquZ/xFHPlY8r+lz5Bg9Zk9ienRhc8SiY=";
+    hash = "sha256-ShH6MDr76wzWQrJvhMWCnklaox/uRsfoe+aYVSo/eNA=";
   };
   npmRoot = "widget";