Work around incomplete std::from_chars support

libc++ (at least the version used in macOS 15) doesn't seem to support
doubles in std::from_chars yet. Hence, we remove the corresponding test
case to avoid compiler errors.

Author: Krzmbrzl

tests/unit/test_utilities.cpp

@@ -15,6 +15,7 @@
 #include <SeQuant/core/utility/strong.hpp>
 #include <SeQuant/core/utility/tensor.hpp>
 
+#include <charconv>
 #include <limits>
 #include <ranges>
 #include <string>
@@ -607,9 +608,6 @@ TEST_CASE("utilities", "[utilities]") {
                    WithinAbs(3.14, std::numeric_limits<float>::epsilon()));
       REQUIRE_THAT(string_to<float>("-3.14159"),
                    WithinAbs(-3.14159, std::numeric_limits<float>::epsilon()));
-      REQUIRE_THAT(
-          string_to<double>("2.7182818284590"),
-          WithinAbs(2.7182818284590, std::numeric_limits<double>::epsilon()));
 
       REQUIRE_THROWS_MATCHES(
           string_to<float>(" 3.14"), ConversionException,