refactor: move memory exporter to v1 package

[fank]

Summary

• Move export types and builder logic into a dedicated v1 package at internal/storage/memory/export/v1/
• Prepare the codebase for creating a v2 export format

Changes

• Create v1/types.go with Export, Time, Entity types
• Create v1/builder.go with Build() function and helper utilities (parseMarkerSize, sideToIndex, boolToInt)
• Simplify export.go to use v1 package for building exports
• Add BuildExport() public method on Backend for thread-safe access
• Update tests to use v1.Export type

New Structure

internal/storage/memory/
├── export.go           (file I/O, uses v1.Export)
├── export_test.go      (updated to use v1.Export)
├── memory.go           (storage backend + BuildExport method)
└── export/
    └── v1/
        ├── types.go    (Export, Time, Entity types)
        └── builder.go  (Build function + helpers)

Test plan

• All existing tests pass
• Full test suite passes

[github-actions]

Merging this branch will increase overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/OCAP2/extension/v5/internal/storage/memory	15.10% (+0.09%)	👍
github.com/OCAP2/extension/v5/internal/storage/memory/export/v1	20.96% (+20.96%)	🌟

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Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/OCAP2/extension/v5/internal/storage/memory/export.go	12.84% (-0.61%)	366 (-1247)	47 (-170)	319 (-1077)	👎
github.com/OCAP2/extension/v5/internal/storage/memory/export/v1/builder.go	20.96% (+20.96%)	1274 (+1274)	267 (+267)	1007 (+1007)	🌟
github.com/OCAP2/extension/v5/internal/storage/memory/export/v1/types.go	0.00% (ø)	0	0	0
github.com/OCAP2/extension/v5/internal/storage/memory/memory.go	15.60% (-1.21%)	1660 (+250)	259 (+22)	1401 (+228)	👎

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.

Changed unit test files

• github.com/OCAP2/extension/v5/internal/storage/memory/export/v1/builder_test.go
• github.com/OCAP2/extension/v5/internal/storage/memory/export_test.go