fix: preserve nested generic element types during hessian2 deserialization (#16440) [3.3]

[waterWang]

What is the purpose of the change?

Fixes #16440 — hessian2 deserialization loses Byte/Short/Float element types in nested generic collections (List<List<Byte>>, Map<String, List<Byte>>), widening them to Integer/Double on the provider side and causing ClassCastException on typed access.

Root cause

hessian2 encodes Byte/Short/Integer all as int and Float/Double as double on the wire, so narrow element types can only be restored from the declared generic type. Two problems combined:

1. Request arguments were decoded (DecodeableRpcInvocation.drawArgs) with only the erased Class, discarding the generic parameter types entirely.
2. Even when a generic Type was available, Hessian2ObjectInput.readObject(Class, Type) ignored it, and hessian-lite's expectedTypes mechanism only handles a single level — nested element types (e.g. the Byte inside Map<String, List<Byte>>) are still widened.

How this is fixed

• MethodDescriptor/ReflectionMethodDescriptor: expose getGenericParameterTypes().
• DecodeableRpcInvocation: capture the generic parameter types when looking up the method and pass them to ObjectInput.readObject(Class, Type).
• Hessian2ObjectInput.readObject(Class, Type): when the declared type is a parameterized collection/map containing narrow wrapper types (Byte/Short/Float/Character), read the object with the erased type and recursively narrow numeric elements to the declared generic element types. Types without narrowable elements (e.g. List<String>) keep the original native path.

Verification

• New unit test testReadObjectWithNestedGenericType in Hessian2SerializationTest covering Map<String, List<Byte>>, List<List<Byte>>, Map<String, List<Float>>, simple List<Byte> and an untouched List<String>.
• mvn -pl dubbo-serialization/dubbo-serialization-hessian2 -am test — all 809 tests pass (incl. 798 TypeMatchTest).
• dubbo-common and dubbo-rpc/dubbo-rpc-dubbo compile.

Checklist

• Make sure there is a GitHub_issue field for the change.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit-test to verify your logic correction.
• Make sure gitHub actions can pass.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 57.57576% with 28 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.92%. Comparing base (5553cb7) to head (268542e).

Files with missing lines	Patch %	Lines
...common/serialize/hessian2/Hessian2ObjectInput.java	54.38%	14 Missing and 12 partials ⚠️
...a/org/apache/dubbo/rpc/model/MethodDescriptor.java	0.00%	1 Missing ⚠️
...bo/rpc/protocol/dubbo/DecodeableRpcInvocation.java	83.33%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                3.3   #16441      +/-   ##
============================================
- Coverage     60.90%   58.92%   -1.98%     
+ Complexity    11765       15   -11750     
============================================
  Files          1953     1953              
  Lines         89271    89335      +64     
  Branches      13473    13497      +24     
============================================
- Hits          54367    52641    -1726     
- Misses        29321    30986    +1665     
- Partials       5583     5708     +125     

Flag	Coverage Δ
integration-tests-java21	?
integration-tests-java8	?
samples-tests-java21	?
samples-tests-java8	?
unit-tests-java11	59.17% <57.57%> (+<0.01%)	⬆️
unit-tests-java17	58.62% <57.57%> (-0.03%)	⬇️
unit-tests-java21	58.63% <57.57%> (-0.01%)	⬇️
unit-tests-java25	58.59% <57.57%> (-0.02%)	⬇️
unit-tests-java8	59.17% <57.57%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.