string: add base argument for ToIntegral to operate on hexadecimal

src/util/strencodings.h

@@ -169,17 +169,18 @@ constexpr inline bool IsSpace(char c) noexcept {
 /**
  * Convert string to integral type T. Leading whitespace, a leading +, or any
  * trailing character fail the parsing. The required format expressed as regex
- * is `-?[0-9]+`. The minus sign is only permitted for signed integer types.
+ * is `-?[0-9]+` by default (or `-?[0-9a-fA-F]+` if base = 16).
+ * The minus sign is only permitted for signed integer types.
  *
  * @returns std::nullopt if the entire string could not be parsed, or if the
  *   parsed value is not in the range representable by the type T.
  */
 template <typename T>
-std::optional<T> ToIntegral(std::string_view str)
+std::optional<T> ToIntegral(std::string_view str, size_t base = 10)
 {
     static_assert(std::is_integral_v<T>);
     T result;
-    const auto [first_nonmatching, error_condition] = std::from_chars(str.data(), str.data() + str.size(), result);
+    const auto [first_nonmatching, error_condition] = std::from_chars(str.data(), str.data() + str.size(), result, base);
     if (first_nonmatching != str.data() + str.size() || error_condition != std::errc{}) {
         return std::nullopt;
     }