fix: fix Java 17 build. No wildcard import.

[suztomo]

The Java 17 build of this repository has been failing. For example #85 (comment)

[INFO] -------------------------------------------------------------
Error:  COMPILATION ERROR : 
[INFO] -------------------------------------------------------------
Error:  /home/runner/work/java-pubsublite-flink/java-pubsublite-flink/src/main/java/com/google/cloud/pubsublite/flink/PubsubLiteSourceSettings.java:[171,23] error: reference to Record is ambiguous
  both class com.google.cloud.pubsublite.flink.internal.reader.Record in com.google.cloud.pubsublite.flink.internal.reader and class java.lang.Record in java.lang match

PubsubLiteSourceSettings was using wildcard import statements that
broke Java 17 build due to the ambiguity with java.lang.Record.

[suztomo]

@dpcollins-google It requires code owner review. Can you check this?