Avoid some build errors

Cargo.toml

@@ -208,3 +208,6 @@ doctest=false
 # RUSTDOCFLAGS="--cfg docsrs" cargo +nightly doc --all-features --no-deps
 all-features = true
 rustdoc-args = ["--cfg", "docsrs"]
+
+[lints.rust]
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(verus_keep_ghost)'] }

src/builtins/utils.rs

@@ -13,8 +13,6 @@ use alloc::collections::{BTreeMap, BTreeSet};
 
 use anyhow::{bail, Result};
 
-use vstd::prelude::*;
-
 #[inline]
 pub fn enforce_limit() -> Result<()> {
     crate::utils::limits::check_memory_limit_if_needed().map_err(anyhow::Error::new)

src/number.rs

@@ -28,14 +28,17 @@ use serde::ser::Serializer;
 use serde::Serialize;
 
 use vstd::prelude::*;
+#[cfg(verus_keep_ghost)]
 use vstd::float::*;
+#[cfg(verus_keep_ghost)]
 use vstd::std_specs::convert::*;
+#[cfg(verus_keep_ghost)]
 use vstd::std_specs::cmp::*;
 
 use crate::*;
+
 use crate::verusspec::bigint::*;
 use crate::verusspec::float::*;
-use crate::verusspec::utils::*;
 
 verus! {