fix: close Java-vs-pymilvus parity gaps and harden V2 APIs

[yhmo]

Close the low-risk, high-value gaps found in the Java-vs-PyMilvus parity audit, plus docs/examples.

Hardening fixes

• getPartitionStats: no longer throws NoSuchElementException when the server omits row_count; numOfEntities falls back to 0L (matching getCollectionStats).
• delete: raises a clear INVALID_PARAMS error instead of an NPE when neither filter nor ids is provided; drop field now requires exactly one of fieldName/fieldId.
• compact: now places collection_name on the wire (ManualCompactionRequest), matching pymilvus.
• getLoadStateV2: returns LoadStateNotExist instead of throwing when the collection does not exist; the legacy Boolean getLoadState keeps throwing since false would mislead as "not loaded". For a non-existent partition the proxy returns a partition-not-found error status, so getLoadStateV2 still throws there, matching pymilvus.

Deprecations (pymilvus parity)

• addCollectionFunction / dropCollectionFunction (and their request classes) are now @Deprecated, replaced by addFunctionField / dropFunctionField.

Missing / partial API parity

• listCompactionTasks: new API listing all retained compaction tasks of a collection (closes the last missing MilvusClientV2 interface); bumps the milvus-proto submodule to expose collection_name on GetCompactionPlansRequest.
• describeRole: GrantInfo.roleName is now populated per grant.
• alterCollectionFunction: adds an explicit functionName member (falls back to Function.getName()).
• getCompactionState / getCompactionPlans: reject a null compaction ID with a clear INVALID_PARAMS error.
• createResourceGroup: accepts a null config (server default); updateResourceGroups: accepts an empty config map.

Docs / examples

• V2 examples for index, alias, partition, database and analyzer APIs.
• AddFieldExample now demonstrates alterCollectionField (e.g. changing max_length).

Tests: mvn -pl sdk-core -o -Pintegration test (2528 unit + integration tests) passes.

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[codecov]

Codecov Report

❌ Patch coverage is 70.00000% with 24 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (master@6e788c6). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...ilvus/v2/service/collection/CollectionService.java	33.33%	8 Missing and 2 partials ⚠️
...ervice/utility/request/ListCompactionTasksReq.java	61.11%	7 Missing ⚠️
...v2/service/resourcegroup/ResourceGroupService.java	66.66%	2 Missing and 1 partial ⚠️
...collection/request/AlterCollectionFunctionReq.java	71.42%	2 Missing ⚠️
...a/io/milvus/v2/service/utility/UtilityService.java	92.30%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #2102   +/-   ##
=========================================
  Coverage          ?   80.86%           
=========================================
  Files             ?      490           
  Lines             ?    30093           
  Branches          ?     3122           
=========================================
  Hits              ?    24334           
  Misses            ?     4447           
  Partials          ?     1312           

Files with missing lines	Coverage Δ
.../main/java/io/milvus/v2/client/MilvusClientV2.java	74.30% <100.00%> (ø)
...e/collection/request/AddCollectionFunctionReq.java	100.00% <ø> (ø)
.../collection/request/DropCollectionFunctionReq.java	100.00% <ø> (ø)
.../milvus/v2/service/partition/PartitionService.java	88.97% <100.00%> (ø)
...in/java/io/milvus/v2/service/rbac/RBACService.java	98.84% <100.00%> (ø)
...ava/io/milvus/v2/service/vector/VectorService.java	89.92% <100.00%> (ø)
...collection/request/AlterCollectionFunctionReq.java	93.75% <71.42%> (ø)
...a/io/milvus/v2/service/utility/UtilityService.java	94.10% <92.30%> (ø)
...v2/service/resourcegroup/ResourceGroupService.java	92.53% <66.66%> (ø)
...ervice/utility/request/ListCompactionTasksReq.java	61.11% <61.11%> (ø)
... and 1 more

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