[FLINK-40157][state/ForSt] Fix MapState putAll value serialization

[Zakelly]

What is the purpose of the change

The ForSt's asyncPutAll uses the wrong serialized form without the null flag, so when reading it gives the wrong.

Brief change log

• Align ForStDBBunchPutRequest.buildSerializedValue with the ForStDBPutRequest's.

Verifying this change

• Added new assertion to check the deserialized value equals the serialized one

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

[Zakelly]

@AlexYinHan Would you please take a look?

[flinkbot]

CI report:

• 06356d3 Azure: SUCCESS

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[AlexYinHan]

@Zakelly Thanks for the fix. LGTM :)