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

lib/strcase.h

@@ -36,6 +36,6 @@ void Curl_strntoupper(char *dest, const char *src, size_t n);
 void Curl_strntolower(char *dest, const char *src, size_t n);
 
 bool Curl_safecmp(const char *a, const char *b);
-int Curl_timestrcmp(const char *first, const char *second);
+int Curl_timestrcmp(const char *a, const char *b);
 
 #endif /* HEADER_CURL_STRCASE_H */