refactor(inkless): SharedState to own StorageBackends

[jeqo]

Refactoring follow up from #467

Properly separating storage back-end clients between read/write and background jobs.
SharedState now owns the StorageBackends lifecycle, properly closing all of them.
So, Reader and Writer component do not have to close storages anymore.

Alongside, making background components internal constructors visible for easier testing.
This allows to make internal SharedState constructor private.

[Copilot]

Pull request overview

This PR refactors the SharedState class to properly own and manage the lifecycle of storage backends, separating them into three dedicated instances for fetch, produce, and background operations. The refactoring also simplifies the MetadataView.getTopicConfig method to directly return LogConfig instead of Properties, eliminating the need for manual config merging in consuming code.

Key changes:

• SharedState now creates and owns three separate StorageBackend instances (fetchStorage, produceStorage, backgroundStorage) and is responsible for closing all of them
• Reader and Writer components no longer close storage backends; SharedState handles all storage lifecycle management
• Background components (FileMerger, FileCleaner) now have package-visible constructors for easier testing
• MetadataView.getTopicConfig() now returns LogConfig directly, with default config merging happening internally

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
storage/inkless/src/main/java/io/aiven/inkless/common/SharedState.java	Refactored to own three separate StorageBackend instances, added comprehensive resource cleanup in close() and exception handlers
storage/inkless/src/main/java/io/aiven/inkless/produce/Writer.java	Removed storage parameter and close logic from internal constructor
storage/inkless/src/main/java/io/aiven/inkless/produce/AppendHandler.java	Simplified to use Function<String, LogConfig> instead of manually merging configs
storage/inkless/src/main/java/io/aiven/inkless/merge/FileMerger.java	Added package-visible constructor for testing, uses backgroundStorage from SharedState
storage/inkless/src/main/java/io/aiven/inkless/delete/FileCleaner.java	Updated to use backgroundStorage from SharedState
storage/inkless/src/main/java/io/aiven/inkless/delete/RetentionEnforcer.java	Simplified to directly use getTopicConfig without manual config merging
storage/inkless/src/main/java/io/aiven/inkless/delete/DeleteRecordsInterceptor.java	Refactored to accept ControlPlane and MetadataView directly instead of SharedState
storage/inkless/src/main/java/io/aiven/inkless/consume/Reader.java	Removed storage close logic
storage/inkless/src/main/java/io/aiven/inkless/consume/FetchHandler.java	Updated to use fetchStorage from SharedState
storage/inkless/src/main/java/io/aiven/inkless/control_plane/MetadataView.java	Changed getTopicConfig return type from Properties to LogConfig
core/src/main/scala/kafka/server/metadata/InklessMetadataView.scala	Implemented new getTopicConfig signature, merging default and topic configs internally
Test files	Updated to reflect new constructor signatures and simplified mocking requirements

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