Use and extend the detail helpers to remove duplicated code

Library:
- binary_reader: format bytes with hex_byte() instead of snprintf
- add throw_type_must_be() for the 20 copies of type_error.302
- binary_reader: add last_byte_error()/unexpected_byte() for the 32
  "parse error at the last read byte" sites (replaces bon8_error)
- json_sax: add check_container_size() for out_of_range.408 and
  diagnostic_positions::set_container_start/_end()
- json_pointer: add throw_no_parent() (405) and throw_unresolved() (404)

Tests:
- unit-class_parser uses the shared utils::SaxCountdown
- move SaxEventLogger (and its ExitAfter* variants) from unit-class_parser
  and unit-deserialization into the new tests/src/test_sax.hpp

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

include/nlohmann/json.hpp

@@ -3266,7 +3266,7 @@ public:
     {
         if (!is_binary())
         {
-            JSON_THROW(type_error::create(302, detail::concat("type must be binary, but is ", type_name()), this));
+            detail::throw_type_must_be("binary", *this);
         }
 
         return *get_ptr<binary_t*>();
@@ -3278,7 +3278,7 @@ public:
     {
         if (!is_binary())
         {
-            JSON_THROW(type_error::create(302, detail::concat("type must be binary, but is ", type_name()), this));
+            detail::throw_type_must_be("binary", *this);
         }
 
         return *get_ptr<const binary_t*>();