Regression test: type dictionary exported once per store commit

[hrstoyanov]

Summary

Regression test for the coalesced type dictionary export (serializer fix in eclipse-serializer/serializer#314).

A single storeRoot serializing a large root graph discovers and registers many distinct types. The type dictionary must be exported exactly once per store commit, not once per registered type — the crash-safe export (temp-file write + fsync + delete + move) is comparatively expensive, so per-type exports made a first store of a ~280-type graph take ~2.9s.

Test

TypeDictionaryExportCoalescingTest:

1. Stores a root graph of 400 entities across 8 distinct types via a counting file-handler decorator.
2. Asserts exactly 1 type dictionary export for the whole storeRoot.
3. Restarts the storage against the same directory and reloads all 400 entities, proving the single coalesced export produced a complete dictionary.

Dependency

Requires the serializer fix in eclipse-serializer/serializer#314 (without it, the test asserts 1 export and fails with ~280).

[hrstoyanov]

@fh-ms @hg-ms @zdenek-jonas
After upgrading to the latest unpublished version if ES, my junit tests started taking 45x the time to run! The PR above (and the one for the serializer) is a quick fix for me to keep my CI/CD usable , and seems correct, but I do think it addresses a real performance degradation introduced recently