chore: Better feedback invalid content topic (#2254)

* typo correction appplication -> application
* content_topic.nim: better feedback to user when wrong topic is passed
* test_namespaced_topics.nim: updating tests accordingly

tests/waku_core/test_namespaced_topics.nim

@@ -89,7 +89,7 @@ suite "Waku Message - Content topics namespacing":
     let err = ns.tryError()
     check:
       err.kind == ParsingErrorKind.InvalidFormat
-      err.cause == "invalid topic structure"
+      err.cause == "Invalid content topic structure. Expected either /<application>/<version>/<topic-name>/<encoding> or /<gen>/<application>/<version>/<topic-name>/<encoding>"
 
   test "Parse content topic string - Invalid string: missing encoding part":
     ## Given
@@ -104,7 +104,7 @@ suite "Waku Message - Content topics namespacing":
     let err = ns.tryError()
     check:
       err.kind == ParsingErrorKind.InvalidFormat
-      err.cause == "invalid topic structure"
+      err.cause == "Invalid content topic structure. Expected either /<application>/<version>/<topic-name>/<encoding> or /<gen>/<application>/<version>/<topic-name>/<encoding>"
 
   test "Parse content topic string - Invalid string: wrong extra parts":
     ## Given

waku/waku_core/topics/content_topic.nim

@@ -74,7 +74,7 @@ proc parse*(T: type NsContentTopic, topic: ContentTopic|string): ParsingResult[N
     of 4:
       let app = parts[0]
       if app.len == 0:
-        return err(ParsingError.missingPart("appplication"))
+        return err(ParsingError.missingPart("application"))
 
       let ver = parts[1]
       if ver.len == 0:
@@ -100,7 +100,7 @@ proc parse*(T: type NsContentTopic, topic: ContentTopic|string): ParsingResult[N
 
       let app = parts[1]
       if app.len == 0:
-        return err(ParsingError.missingPart("appplication"))
+        return err(ParsingError.missingPart("application"))
 
       let ver = parts[2]
       if ver.len == 0:
@@ -116,7 +116,9 @@ proc parse*(T: type NsContentTopic, topic: ContentTopic|string): ParsingResult[N
 
       return ok(NsContentTopic.init(some(gen), app, ver, name, enc))
     else:
-      return err(ParsingError.invalidFormat("invalid topic structure"))
+
+      let errMsg = "Invalid content topic structure. Expected either /<application>/<version>/<topic-name>/<encoding> or /<gen>/<application>/<version>/<topic-name>/<encoding>"
+      return err(ParsingError.invalidFormat(errMsg))
 
 # Content topic compatibility