tokio-xmpp: Ignore missing "version" stream attribute for 0114 components

From the prosody@ room:
- 0114 doesn't mention the removal of @version on the stream, and it
  refers to 3920 which has it as a MUST.
- 0114 streams have historically never used @version="1.0"
- @version="1.0" implies stream features which 0114 doesn't have.
- There was a proposal years ago to fix this but a new XEP was preferred
  (0225).

The change here uses a compile-time check, and may have to change when
support for 0225 arrives if it's still gated behind the "component"
feature (even though it may be weird to have both under the same
feature). We'll see when we get there.

Signed-off-by: pep <pep@bouah.net>

tokio-xmpp/ChangeLog

@@ -1,5 +1,7 @@
 Version NEXT:
 0000-00-00 RELEASER <releaser@domain>
+    * Fixed:
+      - Ignore missing "version" stream attribute for 0114 components.
 
 Version 5.0.0:
 2025-10-28 pep <pep@bouah.net>

tokio-xmpp/src/xmlstream/common.rs

@@ -876,10 +876,12 @@ impl StreamHeader<'static> {
                             }
                         }
                         None => {
-                            return Err(io::Error::new(
-                                io::ErrorKind::InvalidData,
-                                "required `version` attribute missing",
-                            ))
+                            if cfg!(not(feature = "component")) {
+                                return Err(io::Error::new(
+                                    io::ErrorKind::InvalidData,
+                                    "required `version` attribute missing",
+                                ));
+                            }
                         }
                     }