Tests: cover the remaining lines of the library headers

Add tests for the lines of include/nlohmann that were not covered: the
binary readers and writers, the lexer and locale paths, the json_view
modules, the custom number, key and array types, json_pointer, json_patch,
diff and the iterators.

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

tests/src/unit-bon8.cpp

@@ -329,6 +329,9 @@ TEST_CASE("BON8")
             check_bon8({false, nullptr, true}, {0x83, 0xF8, 0xFA, 0xF9});
             check_bon8({false, nullptr, true, 1.0}, {0x84, 0xF8, 0xFA, 0xF9, 0xFD});
             check_bon8({false, nullptr, true, 1.0, json::array(), 0.0}, {0x85, 0xF8, 0xFA, 0xF9, 0xFD, 0x80, 0xFC, 0xFE});
+            // an array that starts with a number: -1, 0, and 1 have bytes of their own
+            check_bon8({-1.0, 0.0, 1.0}, {0x83, 0xFB, 0xFC, 0xFD});
+            check_bon8({1.0, -1.0, -0.0}, {0x83, 0xFD, 0xFB, 0x8E, 0x80, 0x00, 0x00, 0x00});
             check_bon8({{{1}}}, {0x81, 0x81, 0x81, 0x91});
             check_bon8({{{"foo"}}}, {0x81, 0x81, 0x81, 'f', 'o', 'o', 0xFF});
             check_bon8({{{""}}}, {0x81, 0x81, 0x81, 0xFF});