CachedBitGenerator: value_type -> result_type to fix for libcxx

https://reviews.llvm.org/D120630 introduced a __libcpp_random_is_valid_urng
check which requires return value to be in ::result_type (sidenote: that check
goes beyond enforcing
https://en.cppreference.com/w/cpp/numeric/random/uniform_random_bit_generator).
Looking at an arbitrary generator in the standard library
https://en.cppreference.com/w/cpp/numeric/random/independent_bits_engine , it
also provides result_type, not value_type.

external/algorithms/core/include/algorithms/detail/random.h

@@ -17,22 +17,22 @@ namespace algorithms::detail {
 //  Implements the uniform_random_bit_generator concept
 class CachedBitGenerator {
 public:
-  using value_type = uint_fast64_t;
-  using GenFunc    = std::function<std::vector<value_type>(size_t /* N */)>;
+  using result_type = uint_fast64_t;
+  using GenFunc    = std::function<std::vector<result_type>(size_t /* N */)>;
   CachedBitGenerator(const GenFunc& gen, const size_t cache_size)
       // index starts at the end of the (empty) cache to force an immediate refresh
       // on first access
       : m_gen{gen}, m_cache(cache_size), m_index{cache_size} {}
 
-  value_type operator()() {
+  result_type operator()() {
     if (m_index >= m_cache.size()) {
       refresh();
     }
     return m_cache[m_index++];
   }
 
-  static constexpr value_type min() { return 0; }
-  static constexpr value_type max() { return std::numeric_limits<value_type>::max(); }
+  static constexpr result_type min() { return 0; }
+  static constexpr result_type max() { return std::numeric_limits<result_type>::max(); }
 
 private:
   void refresh() {
@@ -41,7 +41,7 @@ class CachedBitGenerator {
   }
 
   GenFunc m_gen;
-  std::vector<CachedBitGenerator::value_type> m_cache;
+  std::vector<CachedBitGenerator::result_type> m_cache;
   size_t m_index;
 };
 

external/algorithms/core/include/algorithms/random.h

@@ -63,7 +63,7 @@ class Generator {
 // by running off a auto-refreshing cached random sequence.
 class RandomSvc : public LoggedService<RandomSvc> {
 public:
-  using value_type = detail::CachedBitGenerator::value_type;
+  using value_type = detail::CachedBitGenerator::result_type;
 
   Generator generator() { return {m_gen, m_cache_size}; }
 // FIXME fix the CMake setup so these are properly found in Gaudi