fix: ServiceInterceptor AllowMultiple not respected due to .Distinct()

[liuhaoyang]

Problem

ServiceInterceptorAttribute declares AllowMultiple = true, but multiple ServiceInterceptorAttribute instances wrapping the same inner interceptor type were being incorrectly deduplicated.

Root Cause

In InterceptorCollector.Collect(), the pipeline ends with:

HandleSort().HandleMultiple()).Distinct().ToArray()

• HandleMultiple() correctly keeps AllowMultiple interceptors and deduplicates non-AllowMultiple ones by type.
• However, the trailing .Distinct() uses Equals() for deduplication.
• ServiceInterceptorAttribute.Equals() compares by _interceptorType, so two instances wrapping the same type are treated as equal.
• Result: ServiceInterceptorAttribute.AllowMultiple = true was effectively ignored.

Fix

Removed .Distinct() since HandleMultiple() already provides the correct deduplication semantics:

• AllowMultiple = true → all instances kept
• AllowMultiple = false → deduplicated by type

Changes

File	Change
src/AspectCore.Core/DynamicProxy/InterceptorCollector.cs	Remove .Distinct() from the Collect pipeline
tests/AspectCore.Tests/Integrate/ServiceInterceptorTests.cs	Updated existing test to expect both interface and class-level [ServiceInterceptor] to execute (2 instead of 1); added test for single-attribute case

Test Results

• All 225 tests pass across net6.0/net7.0/net8.0/net9.0
• Zero regressions

Fixes #325

[liuhaoyang]

关闭此 PR，因为它错误地包含了 PR #334 的变更（分支基于错误的 base 创建）。已重新创建干净的 PR。