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/idn.h

@@ -30,7 +30,7 @@ CURLcode Curl_idnconvert_hostname(struct hostname *host);
 #define USE_IDN
 void Curl_free_idnconverted_hostname(struct hostname *host);
 CURLcode Curl_idn_decode(const char *input, char **output);
-CURLcode Curl_idn_encode(const char *input, char **output);
+CURLcode Curl_idn_encode(const char *puny, char **output);
 #else
 #define Curl_free_idnconverted_hostname(x)
 #define Curl_idn_decode(x) NULL