feat: add url_search_params_reset api

[anonrig]

Adds a new API to reuse the existing std::vector.

Usage:

TEST(ada_c, ada_search_params_reset) {
  ada_url_search_params out;

  std::string_view input = "a=b&c=d&c=e&f=g";
  out = ada_parse_search_params(input.data(), input.size());
  ASSERT_EQ(ada_search_params_size(out), 4);

  std::string_view resetted_value = "a=b";
  ada_search_params_reset(out, resetted_value.data(), resetted_value.size());
  ASSERT_EQ(ada_search_params_size(out), 1);

  ada_free_search_params(out);
  SUCCEED();
}

Fixes #699