Extracts parts of code from submodel_database.go

[FriedJannik]

This PR refactors submodel_database.go

• Split into smaller files with less responsibilities
• Extract Queries into own file

[Copilot]

Pull request overview

This PR refactors the Submodel Repository PostgreSQL persistence layer by extracting previously monolithic logic from submodel_database.go into smaller, responsibility-focused files and by moving SQL construction into a dedicated queries package.

Changes:

• Split persistence logic into dedicated read/write/history/visibility/signing database files.
• Extracted SQL builders from persistence into internal/submodelrepository/persistence/queries/submodel_database_queries.go.
• Updated signing APIs and tests to use separate GetSignedSubmodel and GetSignedSubmodelValueOnly methods instead of a valueOnly boolean parameter.

Reviewed changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
internal/submodelrepository/persistence/submodel_write_database.go	New file containing submodel create/patch/put/delete write logic and related helpers.
internal/submodelrepository/persistence/submodel_visibility.go	New file extracting ABAC visibility checks and formula enforcement helper.
internal/submodelrepository/persistence/submodel_signing.go	New file extracting JWS signing logic into separate full vs value-only methods.
internal/submodelrepository/persistence/submodel_read_database.go	New file containing submodel read/query/list logic and cursor helpers.
internal/submodelrepository/persistence/submodel_history_database.go	New file extracting submodel history append/snapshot helpers.
internal/submodelrepository/persistence/submodel_file_attachment_database.go	New file extracting File attachment CRUD + history-wrapped operations.
internal/submodelrepository/persistence/submodel_element_write_database.go	New file containing submodel element write operations and value-only update logic.
internal/submodelrepository/persistence/submodel_database.go	Reduced to core SubmodelDatabase struct and constructors after extraction.
internal/submodelrepository/persistence/submodel_database_signed_test.go	Updated tests to match new signing method split.
internal/submodelrepository/persistence/submodel_database_query_utils.go	Deleted legacy SQL builder utilities after moving builders to queries package.
internal/submodelrepository/persistence/queries/submodel_database_queries.go	New centralized SQL builder module for submodel persistence.
internal/submodelrepository/api/api_submodel_repository_api_service.go	Updated signing endpoints to call the new signing methods.

Files not reviewed (1)

• internal/submodelrepository/api/api_submodel_repository_api_service.go: Language not supported

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