refactor(struct): consolidate shared graph-core foundations

[imbajin]

Purpose of the PR

Server core and Struct currently keep separate implementations of IDs, schema, queries and codecs. A fix can land in one copy while callers continue using the other. This PR gives those shared types one implementation in Struct, keeps graph execution in Core, and removes graph-engine dependencies from PD and Store.

For example, both Server and Store will use org.apache.hugegraph.id.IdGenerator; the old Core copy is removed. Core still owns transactions, traversal and backend adapters.

Shared ownership only; the diagram omits client and runtime dependencies. Core still uses PD/Store clients for HStore execution.

Related to hugegraph#257. Earlier review is in hugegraph/hugegraph#260.

Main Changes

Area	What changes	What to review
Shared types	Struct owns IDs, schema metadata, queries, base elements, indexes, analyzers and codecs	Callers use one implementation; Core wrappers retain engine callbacks and one shared element state
Service responsibilities	Store owns PD-backed schema connections, watches and cache lifecycle; Common owns JWT helpers and RPC configuration contracts	Resource cleanup, namespace handling and service-specific failure responses
Java API and SPI	Types move packages; signatures such as sameAs and index serialization use shared types	Update implementations and callers, then recompile integrations
Historical data	Readers recognize supported old Java class names and enum ordinals	Frozen producer fixtures and streamed Kryo decoding; canonical writer formats stay stable
Behavioral repairs	String IDs use consistent UTF-16 ordering; schema key order is preserved; HStore OLAP keys include the property ID	These changes deserve separate review from package moves

What developers need to do

This prepares the planned 1.8.0 migration without changing release version numbers.

If you…	Required action
Maintain a Java plugin or integration using the moved types	Update imports and affected method signatures, then rebuild against matching artifacts. Old compiled plugins are not binary-compatible
Deploy Server, PD and Store	Upgrade them together and match their PD metadata namespace. Mixed-version rolling upgrades are unsupported
Used Store-side rebuilding of long-text indexes	Assess and rebuild affected indexes from graph data. Old shortened keys may not match full-value queries; this PR does not rebuild them automatically
Use HStore OLAP properties	New rows use (property ID, vertex ID). Reads fall back only to matching legacy rows; values already overwritten by the old writer cannot be recovered

The migration guide includes the API mapping, configuration examples and compatibility details. Affected Toolchain and Computer callers require matching artifacts and their own build/classpath validation before release.

Verifying these changes

• Trivial rework / code cleanup without test coverage.
• Existing engine, analyzer, PD/Store and API tests, plus focused shared-type and historical-data regressions.
• Additional validation with resolved dependency trees and actual packaged classpaths.

Rebased on current master after #3263 merged, retaining its GraphBinary Schema/Blob, GraphSON V1 Tree, GValue/ID predicate, named range/count, DATE and kubeconfig compatibility repairs. Shared-type references now use their canonical Struct owners; the current CI policy is retained.

CI builds now install concrete parent versions for Maven 3.10, and benchmark packaging preserves the flattened test POM. Cluster tests use matching Commons with the existing client. Task cancellation waits for actual script progress, and unused PowerMock dependencies and their release entries are removed.

Local Java 17 compilation, shared-type/historical-codec regressions, Server unit tests, focused Memory/RocksDB query regressions and Store ingress/schema tests are validated against this integrated tree. Fresh service distributions are checked for duplicate HugeGraph classes and their actual runtime/nested dependency inventory. Upstream CI and full TinkerPop/HStore qualification on the updated head remain required before merging.

Does this PR potentially affect the following parts?

• Dependencies: resolved versions, packaged class ownership, inventory and license coverage.
• Modify configurations: Store PD namespace and Gremlin class imports.
• The public API: Java/SPI types and method descriptors.
• Other affects: documented index and OLAP behavior.
• Nope

Documentation Status

• Doc - TODO
• Doc - Done: in-repository guide and paired bilingual apache/hugegraph-doc#511.
• Doc - No Need

Coordinate code and website merges, then complete downstream delivery before release.

[codecov]

Codecov Report

❌ Patch coverage is 53.67847% with 170 lines in your changes missing coverage. Please review.
✅ Project coverage is 41.18%. Comparing base (d9abcd4) to head (704b980).

Files with missing lines	Patch %	Lines
...hugegraph/backend/serializer/BinarySerializer.java	47.91%	18 Missing and 7 partials ⚠️
.../java/org/apache/hugegraph/structure/HugeEdge.java	58.62%	17 Missing and 7 partials ⚠️
...ava/org/apache/hugegraph/structure/HugeVertex.java	65.21%	19 Missing and 5 partials ⚠️
...he/hugegraph/backend/tx/GraphIndexTransaction.java	44.73%	19 Missing and 2 partials ⚠️
...va/org/apache/hugegraph/structure/HugeElement.java	61.53%	17 Missing and 3 partials ⚠️
...che/hugegraph/schema/builder/EdgeLabelBuilder.java	0.00%	8 Missing ⚠️
...n/java/org/apache/hugegraph/auth/HugeResource.java	0.00%	6 Missing ⚠️
...gegraph/backend/store/memory/InMemoryDBTables.java	16.66%	5 Missing ⚠️
.../apache/hugegraph/backend/tx/GraphTransaction.java	20.00%	3 Missing and 1 partial ⚠️
...a/org/apache/hugegraph/structure/HugeProperty.java	69.23%	1 Missing and 3 partials ⚠️
... and 18 more

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3270      +/-   ##
============================================
+ Coverage     41.03%   41.18%   +0.15%     
+ Complexity     7239     6772     -467     
============================================
  Files           788      766      -22     
  Lines         68451    66086    -2365     
  Branches       9256     8773     -483     
============================================
- Hits          28087    27217     -870     
+ Misses        37090    35821    -1269     
+ Partials       3274     3048     -226     

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