Fix Wformat compiler warnings

[ccotter]

examples/linux/http_server_io_uring_test.cpp: In function 'unifex::task<{anonymous}::Request> {anonymous}::parse_request(unifex::linuxos::io_uring_context::async_read_write_file&)':
examples/linux/http_server_io_uring_test.cpp:99:34: error: format '%ld' expects argument of type 'long int', but argument 2 has type 'std::basic_string<char>::size_type' {aka 'unsigned int'} [-Werror=format=]
   99 |       std::printf("req too big=%ld\n", req.size());
      |                                ~~^     ~~~~~~~~~~
      |                                  |             |
      |                                  long int      std::basic_string<char>::size_type {aka unsigned int}
      |                                %d
examples/linux/http_server_io_uring_test.cpp: In lambda function:
examples/linux/http_server_io_uring_test.cpp:160:54: error: format '%ld' expects argument of type 'long int', but argument 2 has type 'std::chrono::duration<long long int, std::ratio<1, 1000> >::rep' {aka 'long long int'} [-Werror=format=]
  160 |             then([ms] { std::printf("Timeout after %ldms\n", ms.count()); }),
      |                                                    ~~^       ~~~~~~~~~~
      |                                                      |               |
      |                                                      long int        std::chrono::duration<long long int, std::ratio<1, 1000> >::rep {aka long long int}
      |                                                    %lld

[ispeters]

Thanks for the PR! I like the intent and want to merge it, but it seems there are some broken CI jobs that'll need fixing first.