Update Colvars library to version 2025-04-18

The following is a list of pull requests relevant to LAMMPS in the Colvars repository since 2024-08-06:

- 752 New tool poisson_integrator_conv
  https://github.com/Colvars/colvars/pull/752 (@jhenin)

- 733 Custom grids for all biases
  https://github.com/Colvars/colvars/pull/733 (@giacomofiorin, @jhenin)

- 776 Avoid error in acos and asin with fast-math
  https://github.com/Colvars/colvars/pull/776 (@jhenin)

- 773 fix: fix the clang build test failure of OPES
  https://github.com/Colvars/colvars/pull/773 (@HanatoK)

- 768 fix: clamp the input values of asin and acos in case of fast math on aarch64
  https://github.com/Colvars/colvars/pull/768 (@HanatoK)

- 761 Add debug code for the Jacobi failure
  https://github.com/Colvars/colvars/pull/761 (@HanatoK)

- 759 min_image fix; Saves long runs from crashes;
  https://github.com/Colvars/colvars/pull/759 (@PolyachenkoYA)

- 757 Fix MSVC OpenMP issue
  https://github.com/Colvars/colvars/pull/757 (@HanatoK)

- 755 Fix indentation of 'Init CVC' message in standard output
  https://github.com/Colvars/colvars/pull/755 (@jhenin)

- 750 Optimize and simplify the calculation of dihedral gradients
  https://github.com/Colvars/colvars/pull/750 (@HanatoK)

- 749 Add references to new Colvars paper
  https://github.com/Colvars/colvars/pull/749 (@jhenin, @giacomofiorin)

- 740 Report the specific C++ standard at init time, stop warning about C++97/03
  https://github.com/Colvars/colvars/pull/740 (@giacomofiorin)

- 731 Improve detection of hard/mathematical boundaries
  https://github.com/Colvars/colvars/pull/731 (@giacomofiorin)

- 729 Optimize the fit gradients
  https://github.com/Colvars/colvars/pull/729 (@HanatoK, @jhenin)

- 728 Fix undefined behavior when getting the current working directory from std::filesystem
  https://github.com/Colvars/colvars/pull/728 (@giacomofiorin)

- 727 Add patchversion scripting command
  https://github.com/Colvars/colvars/pull/727 (@giacomofiorin)

- 724 Fix gradients and metric functions of distanceDir
  https://github.com/Colvars/colvars/pull/724 (@giacomofiorin)

- 715 Add missing rotation in orientation component
  https://github.com/Colvars/colvars/pull/715 (@giacomofiorin)

- 713 fix: try to solve #87 for non-scala components
  https://github.com/Colvars/colvars/pull/713 (@HanatoK)

- 709 Implementation of OPES in Colvars
  https://github.com/Colvars/colvars/pull/709 (@HanatoK, @giacomofiorin, @jhenin)

- 706 BUGFIX for Segmentation fault in colvarbias_meta::calc_energy() with useGrids off
  https://github.com/Colvars/colvars/pull/706 (@alphataubio)

- 570 enable use of CVs defined by PyTorch neural network models
  https://github.com/Colvars/colvars/pull/570 (@zwpku, @giacomofiorin, @HanatoK, @jhenin)

Authors: @alphataubio, @EzryStIago, @giacomofiorin, @HanatoK, @jhenin, @PolyachenkoYA, @zwpku

lib/colvars/colvarproxy_io.cpp

@@ -7,10 +7,28 @@
 // If you wish to distribute your changes, please submit them to the
 // Colvars repository at GitHub.
 
+
+#if defined(_WIN32) && !defined(__CYGWIN__)
+
 // Using access() to check if a file exists (until we can assume C++14/17)
-#if !defined(_WIN32) || defined(__CYGWIN__)
-#include <unistd.h>
+#include <direct.h>
+
+#if defined(__has_include)
+# if __has_include(<filesystem>)
+#  include <filesystem> // MSVC only defines __cpp_lib_filesystem after include
+# endif
 #endif
+
+#else
+
+#include <unistd.h>
+
+#ifdef __cpp_lib_filesystem
+#include <filesystem>
+#endif
+
+#endif
+
 #if defined(_WIN32)
 #include <io.h>
 #endif
@@ -64,6 +82,53 @@ int colvarproxy_io::set_frame(long int)
 }
 
 
+std::string colvarproxy_io::get_current_work_dir() const
+{
+#ifdef __cpp_lib_filesystem
+
+  return std::filesystem::current_path().string();
+
+#else
+
+  // Legacy code
+  size_t constexpr buf_size = 3001;
+  char buf[buf_size];
+
+#if defined(_WIN32) && !defined(__CYGWIN__)
+  char *getcwd_result = ::_getcwd(buf, buf_size);
+#else
+  char *getcwd_result = ::getcwd(buf, buf_size);
+#endif
+
+  if (getcwd_result == nullptr) {
+    cvm::error("Error: cannot read the current working directory.\n", COLVARS_INPUT_ERROR);
+    return std::string("");
+  }
+
+  return std::string(getcwd_result);
+#endif
+}
+
+
+std::string colvarproxy_io::join_paths(std::string const &path1, std::string const &path2) const
+{
+#ifdef __cpp_lib_filesystem
+
+  return (std::filesystem::path(path1) / std::filesystem::path(path2)).string();
+
+#else
+
+  // Legacy code
+#if defined(_WIN32) && !defined(__CYGWIN__)
+  return (path1 + "\\" + path2);
+#else
+  return (path1 + "/" + path2);
+#endif
+
+#endif
+}
+
+
 int colvarproxy_io::backup_file(char const *filename)
 {
   // Simplified version of NAMD_file_exists()