Require a recent cxx version

Author: Chris00

crates/mfem-sys/Cargo.toml

@@ -10,7 +10,7 @@ repository = "https://github.com/mkovaxx/mfem-rs"
 rust-version = "1.77"
 
 [dependencies]
-cxx = "1"
+cxx = "1.0.137"
 autocxx = "0.27"
 
 [build-dependencies]

crates/mfem/Cargo.toml

@@ -9,7 +9,7 @@ edition = "2021"
 repository = "https://github.com/mkovaxx/mfem-rs"
 
 [dependencies]
-cxx = "1"
+cxx = "1.0.137"
 mfem-sys = { version = "0.2.0", path = "../mfem-sys" }
 thiserror = "1.0.59"