lib: optimize struct layouts for reduced memory usage

struct SingleRequest tweaks

- 'upgr101' from enum upgrade101 => 'unsigned char', saves three bytes
- made some 'unsigned char' => uint8_t
- moved 'io_flags' to fill a hole on 64-bit arch

struct UserDefined tweaks

- Sort the fields by size. Larger to smaller. Helps avoding holes.
- httpsig_algorithm moved
- FTP uint8_t fields moved
- new_file_perms moved
- rtspreq moved
- sort fields on size

- urldata: drop 'struct Curl_data_priority'

  It only had a single struct member 'weight'. Use that directly instead
  to save indirections and struct alignments. Move field for size order.

- urldata: move the RTSP fields in the UrlState struct to be ordered by
  size

struct PureInfo tweaks

- make 'pxcode' a uint8_t
- move 'conn_protocol' to fill a hole
- sort 'struct PureInfo' fields by size

Closes #22585

lib/http2.c

@@ -704,7 +704,7 @@ static struct Curl_easy *h2_duphandle(struct Curl_cfilter *cf,
   if(second) {
     struct h2_stream_ctx *second_stream;
     http2_data_setup(cf, second, &second_stream);
-    second->state.priority.weight = data->state.priority.weight;
+    second->state.weight = data->state.weight;
     if(data->share)
       (void)Curl_share_easy_link(second, data->share);
   }
@@ -1757,15 +1757,15 @@ out:
 static int sweight_wanted(const struct Curl_easy *data)
 {
   /* 0 weight is not set by user and we take the nghttp2 default one */
-  return data->set.priority.weight ?
-    data->set.priority.weight : NGHTTP2_DEFAULT_WEIGHT;
+  return data->set.weight ?
+    data->set.weight : NGHTTP2_DEFAULT_WEIGHT;
 }
 
 static int sweight_in_effect(const struct Curl_easy *data)
 {
   /* 0 weight is not set by user and we take the nghttp2 default one */
-  return data->state.priority.weight ?
-    data->state.priority.weight : NGHTTP2_DEFAULT_WEIGHT;
+  return data->state.weight ?
+    data->state.weight : NGHTTP2_DEFAULT_WEIGHT;
 }
 
 /*
@@ -1777,10 +1777,9 @@ static int sweight_in_effect(const struct Curl_easy *data)
 static void h2_pri_spec(struct Curl_easy *data,
                         nghttp2_priority_spec *pri_spec)
 {
-  struct Curl_data_priority *prio = &data->set.priority;
-  nghttp2_priority_spec_init(pri_spec, 0,
-                             sweight_wanted(data), FALSE);
-  data->state.priority = *prio;
+  int prio = data->set.weight;
+  nghttp2_priority_spec_init(pri_spec, 0, sweight_wanted(data), FALSE);
+  data->state.weight = prio;
 }
 
 /*