clang-tidy: sync argument names in prototype and definition

Discovered with clang-tidy checker
`readability-inconsistent-declaration-parameter-name`.

Also:
- do not enforce the above because of inconsistencies still present
  between public API prototypes and definitions. (Also betwen man page
  protos, and man page examples, and other parts of the code, e.g.
  `easy` vs `curl` vs `d` vs `handle`) Perhaps subject for a future
  effort:
  https://github.com/curl/curl/actions/runs/22166472728/job/64094691653
- enable and fix `readability-named-parameter` where missing.

Refs:
https://clang.llvm.org/extra/clang-tidy/checks/readability/inconsistent-declaration-parameter-name.html
https://clang.llvm.org/extra/clang-tidy/checks/readability/named-parameter.html

Closes #20624

tests/libtest/first.h

@@ -82,7 +82,7 @@ int cgetopt(int argc, const char * const argv[], const char *optstring);
 extern int select_wrapper(int nfds, fd_set *rd, fd_set *wr, fd_set *exc,
                           struct timeval *tv);
 
-extern char *hexdump(const unsigned char *buffer, size_t len);
+extern char *hexdump(const unsigned char *buf, size_t len);
 
 #ifndef CURL_DISABLE_WEBSOCKETS
 CURLcode ws_send_ping(CURL *curl, const char *send_payload);