fix: some bugs in DNS proxy

[toxeh]

• main.c: fix NULL pointer dereference in https_resp_cb() — req was used before NULL check, and FLOG also dereferenced NULL req->tx_id
• main.c: fix potential crash in get_host_from_uri() — strlen(host) was called before checking curl_url_get() return code, host could be NULL
• dns_server_tcp.c: fix data corruption on EAGAIN — sent += len was executed with len == -1 when EAGAIN/EWOULDBLOCK occurred, causing negative offset; added continue to skip the addition
• dns_server_tcp.c: fix format string mismatches in FLOG() calls — format had 2 specifiers but 4 arguments were passed (ipstr, port, strerror, errno); changed format to include all 4 arguments
• dns_server_tcp.c: fix typo 'listaning' -> 'listening'
• https_client.c: remove deprecated CURLPIPE_HTTP1 (since libcurl 7.62.0), keep only CURLPIPE_MULTIPLEX