rustls: Fix two warnings related to number types found by @gvanem

[kpcyrd]

Followup for #12989 to fix these two warnings:

vtls/rustls.c(295,53): warning: format specifies type 'long' but the argument has type 'size_t' (aka 'unsigned long long') [-Wformat]
  295 |   CURL_TRC_CF(data, cf, "cf_send: %ld plain bytes", plainlen);
      |                                   ~~~               ^~~~~~~~
      |                                   %zu
./curl_trc.h(79,38): note: expanded from macro 'CURL_TRC_CF'
   79 |          Curl_trc_cf_infof(data, cf, __VA_ARGS__); } while(0)
      |                                      ^~~~~~~~~~~
vtls/rustls.c(411,23): warning: incompatible function pointer types passing 'enum rustls_result (void *, const rustls_verify_server_cert_params *)' (aka
      'enum rustls_result (void *, const struct rustls_verify_server_cert_params *)') to parameter of type 'rustls_verify_server_cert_callback' (aka
      'unsigned int (*)(void *, const struct rustls_verify_server_cert_params *)') [-Wincompatible-function-pointer-types-strict]
  411 |       config_builder, cr_verify_none);
      |                       ^~~~~~~~~~~~~~
f:/MinGW32/src/inet/Crypto/RusTls/src\rustls.h(1272,114): note: passing argument to parameter 'callback' here
 1272 |                                                                               rustls_verify_server_cert_callback callback);
      |                                                                                                                  ^
2 warnings generated.

The patch was suggested by @gvanem.

[bagder]

Thanks!