[REVIEW] Refactor read_sam_byte_vector

include/seqan3/io/sam_file/format_sam.hpp

@@ -850,13 +850,14 @@ inline void format_sam::read_sam_byte_vector(seqan3::detail::sam_tag_variant & v
     if (str.size() % 2 != 0)
         throw format_error{"[CORRUPTED SAM FILE]  Hexadecimal tag must have even number of digits."};
 
-    for (size_t i = 0; i < str.size(); i += 2)
+    // H encodes bytes in a hexadecimal format. Two hex values are stored for each byte as characters.
+    // E.g., '1' and 'A' need one byte each and are read as `\x1A`, which is 27 in decimal.
+    for (auto hex_begin = str.begin(), hex_end = str.begin() + 2; hex_begin != str.end(); hex_begin += 2, hex_end += 2)
     {
-        auto res = std::from_chars(str.begin() + i, str.begin() + i + 2, dummy_byte, 16);
+        auto res = std::from_chars(hex_begin, hex_end, dummy_byte, 16);
 
         if (res.ec == std::errc::invalid_argument)
-            throw format_error{std::string("[CORRUPTED SAM FILE] The string '")
-                               + std::string(str.begin() + i, str.begin() + i + 2)
+            throw format_error{std::string("[CORRUPTED SAM FILE] The string '") + std::string(hex_begin, hex_end)
                                + "' could not be cast into type uint8_t."};
 
         if (res.ec == std::errc::result_out_of_range)