A temporary solution, based on the following:

- introducing a new env variable ZINGG_DRY_RUN
- if the variable is set:
  + mimic globally used JVM-stuff
  + otherwise do nothing

++ slightly update ignore and docs/Makefile
++ apply formatting to client.py

 On branch 762-fix_sphinx_build
 Changes to be committed:
	modified:   .gitignore
	modified:   python/docs/Makefile
	new file:   python/pyproject.toml
	modified:   python/zingg/client.py

Make sphinx works

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	modified:   python/requirements.txt
	new file:   python/zingg_v2/__init__.py
	new file:   python/zingg_v2/client.py
	new file:   python/zingg_v2/errors.py
	new file:   python/zingg_v2/structs.py

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	modified:   python/zingg_v2/structs.py

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	deleted:    python/zingg_v2/client.py
	new file:   python/zingg_v2/pipes.py
	modified:   python/zingg_v2/structs.py

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	modified:   python/pyproject.toml
	new file:   python/zingg_v2/client.py
	modified:   python/zingg_v2/errors.py
	new file:   python/zingg_v2/models.py
	modified:   python/zingg_v2/pipes.py
	deleted:    python/zingg_v2/structs.py

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	modified:   python/zingg_v2/models.py
	modified:   python/zingg_v2/pipes.py

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	new file:   buf.gen.yaml
	new file:   buf.work.yaml
	new file:   protobuf/connect_plugins.proto
	modified:   python/zingg_v2/client.py
	new file:   python/zingg_v2/connect.py
	modified:   python/zingg_v2/models.py
	new file:   python/zingg_v2/proto/connect_plugins_pb2.py
	new file:   python/zingg_v2/proto/connect_plugins_pb2.pyi
	new file:   python/zingg_v2/proto/connect_plugins_pb2_grpc.py

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	modified:   python/zingg_v2/client.py

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	modified:   .gitignore
	modified:   buf.gen.yaml
	modified:   common/core/src/main/java/zingg/common/core/executor/LabelUpdater.java
	modified:   protobuf/connect_plugins.proto
	modified:   python/pyproject.toml
	modified:   python/zingg_v2/client.py
	modified:   python/zingg_v2/models.py
	modified:   python/zingg_v2/proto/connect_plugins_pb2.py
	new file:   scripts/get-spark-connect-local.sh
	new file:   scripts/run-spark-connect-local.sh
	new file:   spark/client/src/main/java/zingg/spark/connect/ZinggConnectPlugin.java
	new file:   spark/client/src/main/java/zingg/spark/connect/proto/ConnectPlugins.java
	new file:   spark/client/src/main/java/zingg/spark/connect/proto/SubmitZinggJob.java
	new file:   spark/client/src/main/java/zingg/spark/connect/proto/SubmitZinggJobOrBuilder.java
	modified:   spark/pom.xml

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	modified:   buf.gen.yaml
	new file:   python/test_spark_connect.py
	modified:   python/zingg_v2/client.py
	modified:   python/zingg_v2/models.py
	modified:   scripts/run-spark-connect-local.sh
	deleted:    spark/client/src/main/java/zingg/spark/connect/ZinggConnectPlugin.java
	new file:   spark/client/src/main/scala/zingg/spark/connect/ZinggConnectPlugin.scala
	modified:   spark/pom.xml

 Untracked files:
	spark-3.5.1-bin-hadoop3.tgz
	spark-3.5.1-bin-hadoop3/

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 Changes to be committed:
	modified:   .gitignore
	modified:   python/requirements.txt
	modified:   python/test_spark_connect.py
	modified:   python/zingg_v2/client.py
	modified:   python/zingg_v2/errors.py
	modified:   scripts/run-spark-connect-local.sh
	modified:   spark/client/pom.xml
	modified:   spark/client/src/main/scala/zingg/spark/connect/ZinggConnectPlugin.scala
	modified:   spark/pom.xml

+ drop scala from spark-client
+ rewrite plugin in java
+ update to scala 2.13 and corresponding fixes
+ small changes

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	modified:   pom.xml
	modified:   spark/client/pom.xml
	new file:   spark/client/src/main/java/zingg/spark/connect/ZinggConnectPlugin.java
	deleted:    spark/client/src/main/scala/zingg/spark/connect/ZinggConnectPlugin.scala
	modified:   spark/core/src/main/java/zingg/spark/core/block/SparkBlockFunction.java
	modified:   spark/core/src/test/java/zingg/TestUDFDoubleWrappedArr.java