Reapply "refactor: reduce Reservoir build fetch attempts & warnings (#…

…5600)"

This reverts commit 1cf7623.

Revert "feat: lake: Reservoir build cache (#5486)"

This reverts commit ffb4c5b.

Revert "feat: lake: Reservoir build cache (#5486)"

This reverts commit ffb4c5b.

chore: update CMakeLists.txt

chore: set LEAN_VERSION_IS_RELEASE

chore: use `Expr.numObjs` instead of `lean_expr_size_shared` (#5239)

Remark: declarations like `sizeWithSharing` must be in `IO` since they
are not functions.

The commit also uses the more efficient `ShareCommon.shareCommon'`.

chore: release notes for 4.11.0 (#5186)

chore: import Std.Data.HashMap in backported files

chore: adapt stdlib to new `variable` behavior

update CMakeLists.txt