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/features/arbitrary_types.md

@@ -54,7 +54,7 @@ assert(p == p2);
 To make this work with one of your types, you only need to provide two functions:
 
 ```cpp
-using json = nlohmann::json;
+using nlohmann::json;
 
 namespace ns {
     void to_json(json& j, const person& p) {

docs/mkdocs/docs/features/assertions.md

@@ -37,7 +37,7 @@ See also the documentation on [element access](element_access/index.md).
     ```cpp
     #include <nlohmann/json.hpp>
     
-    using json = nlohmann::json;
+    using nlohmann::json;
     
     int main()
     {
@@ -59,7 +59,7 @@ See also the documentation on [element access](element_access/index.md).
     ```cpp
     #include <nlohmann/json.hpp>
     
-    using json = nlohmann::json;
+    using nlohmann::json;
     using namespace nlohmann::literals;
     
     int main()
@@ -87,7 +87,7 @@ uninitialized iterator is undefined behavior and yields a runtime assertion.
     ```cpp
     #include <nlohmann/json.hpp>
     
-    using json = nlohmann::json;
+    using nlohmann::json;
     
     int main()
     {
@@ -114,7 +114,7 @@ behavior and yields a runtime assertion.
     ```cpp
     #include <nlohmann/json.hpp>
     
-    using json = nlohmann::json;
+    using nlohmann::json;
     
     int main()
     {
@@ -146,7 +146,7 @@ result in undefined behavior. Since version 3.12.0, this library checks for `nul
     #include <iostream>
     #include <nlohmann/json.hpp>
     
-    using json = nlohmann::json;
+    using nlohmann::json;
     
     int main()
     {

docs/mkdocs/docs/features/modules.md

@@ -15,7 +15,7 @@ When using modules rather than headers, the previous example for creating a `jso
 import std;
 import nlohmann.json;
 
-using json = nlohmann::json;
+using nlohmann::json;
 
 // ...
 

docs/mkdocs/docs/features/object_order.md

@@ -12,7 +12,7 @@ The default type `nlohmann::json` uses a `std::map` to store JSON objects, and t
     #include <iostream>
     #include <nlohmann/json.hpp>
     
-    using json = nlohmann::json;
+    using nlohmann::json;
     
     int main()
     {