feat(pj_datastore): in-place dataset replace primitives (replaceDatasetFrom) for reload

[facontidavide]

Summary

Adds DataEngine::replaceDatasetFrom and ObjectStore::replaceDatasetFrom — primitives that swap a dataset's data in place while keeping its DatasetId / TopicId / ObjectTopicId stable. This lets a host (PlotJuggler 4) implement data reload as a true replace: refresh a dataset's data without orphaning anything keyed by those ids (plot curve keys, 2D object-dock bindings).

What & how

• DataEngine::replaceDatasetFrom(staged, staged_id, primary_id) — match staged↔primary topics by name. Matched topics: clear the primary's chunks and move the staged topic's chunks in, re-stamping each TopicChunk.topic_id to the primary id (+ move the inline column layout). Staged-only topics: created under the primary dataset. Primary-only topics: retired — chunks cleared, id hidden from listTopics, but the TopicStorage kept so an in-flight reader pointer hits an empty deque rather than freed memory (the engine is append-only; this is the honest "logical removal").
• ObjectStore::replaceDatasetFrom(...) — same on the object side, preserving the primary ObjectTopicId; returns the staged→primary id map so the host re-registers object parsers under stable ids.
• Both reuse the existing cross-store move seams: a new private DataEngine::adoptChunksFrom now single-sources the chunk-deque move shared with flushTo; ObjectStore::eraseTopicLocked is shared by removeTopic and the replace path.
• replace_result.hpp: DatasetReplaceResult / ObjectDatasetReplaceResult.

Tests

7 new unit tests (engine_integration_test, object_store_test): chunk move + topic_id rewrite, added/retired topics, id stability (reader sees new data under the same id); object entry move + ObjectTopicId preservation, removed/added topics. All pass; the existing flushTo tests confirm the adoptChunksFrom unification is safe.

Versioning / ABI

Additive API only (DataEngine/ObjectStore are pimpl; no vtable/struct/C-ABI changes) → a MINOR bump 0.5.1 → 0.6.0. pj_base/abi/baseline.abi is unchanged — the additions live in pj_datastore, outside the pj_base ABI canary.

Consumed by PlotJuggler/PJ4#124 (reload = in-place replace).

🤖 Generated with Claude Code

[facontidavide]

@copilot fix pre-commit

[Copilot]

@copilot fix pre-commit

Fixed in 0664a92 by applying the required clang-format pre-commit formatting updates. Pre-commit now passes.

[facontidavide]

Superseded by the pj_datastore extraction (#113/#114). The datastore primitives in this PR were re-landed in the app repo as PlotJuggler/PJ4#124 (identical content — all 7 source/test files are byte-for-byte the same); closing as obsolete. The only parts not carried over were the SDK-local 0.5.1 → 0.6.0 version bump in CMakeLists.txt/conanfile.py, which were superseded by the actual 0.6.0 release in #113/#114 and the plotjuggler_core → plotjuggler_sdk rename.