Document clang-tidy exclusions, drop unneeded ones, and clean up doc examples (#5909)

* Document clang-tidy exclusions and drop unneeded ones

Re-enable every excluded check in a run of clang-tidy 22 over all tests
and remove the seven that never fire (cert-err58-cpp,
clang-analyzer-webkit.NoUncountedMemberChecker,
cppcoreguidelines-virtual-class-destructor, google-readability-function-size,
hicpp-function-size, hicpp-no-assembler, readability-function-size).

Document the reason for every remaining exclusion at the top of the file.

Exclude in advance the checks that only exist in clang-tidy 23 and are
noise here (bugprone-signed-bitwise, *-explicit-constructor,
readability-trailing-comma, modernize-use-string-view), plus
modernize-use-integer-sign-comparison, which needs C++20 std::cmp_less
and flags deliberate casts.

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

* Fix clang-tidy findings in documentation examples and replace redundant aliases

Apply clang-tidy fixes to the documentation examples:
- performance-avoid-endl: std::endl -> '\n'
- readability-qualified-auto: auto -> auto* / const auto*
- performance-for-range-copy: copy -> const reference
- google-readability-casting: C-style cast -> static_cast

Replace redundant aliases (readability-redundant-qualified-alias) such as
"using json = nlohmann::json;" with "using nlohmann::json;" in the
documentation, README, examples, tests, and benchmarks. Aliases at class
scope and aliases of other types (with_base_class_t etc.) are kept.

No changes to the library or its public API. All changed examples were
compiled and run; their output matches the stored .output files (except
max_size and meta, which depend on the platform and compiler).

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

* Format doc examples with the pinned astyle

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

---------

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

docs/mkdocs/docs/examples/sax_no_exception.cpp

@@ -1,7 +1,7 @@
 #include <iostream>
 #include <nlohmann/json.hpp>
 
-using json = nlohmann::json;
+using nlohmann::json;
 
 // a DOM parser that reports parse errors instead of throwing
 class sax_no_exception : public nlohmann::detail::json_sax_dom_parser<json, nlohmann::detail::string_input_adapter_type>
@@ -18,7 +18,7 @@ class sax_no_exception : public nlohmann::detail::json_sax_dom_parser<json, nloh
         std::cout << "parse error at input byte " << position << "\n"
                   << ex.what() << "\n"
                   << "last read: \"" << last_token << "\""
-                  << std::endl;
+                  << '\n';
         return false;
     }
 };
@@ -33,8 +33,8 @@ int main()
     bool parse_result = json::sax_parse(myinput, &sax);
     if (!parse_result)
     {
-        std::cout << "parsing unsuccessful!" << std::endl;
+        std::cout << "parsing unsuccessful!" << '\n';
     }
 
-    std::cout << "parsed value: " << result << std::endl;
+    std::cout << "parsed value: " << result << '\n';
 }