fix: restrict SentinelResourceAspect pointcut to execution join points

[daguimu]

Problem

When using native AspectJ (compile-time or load-time weaving) instead of Spring AOP, the @SentinelResource annotation aspect fires twice for the same method call on the same thread — once at the call join point and once at the execution join point. This causes SphU.entry() to be called twice, doubling the thread count tracked by Sentinel and resulting in incorrect thread-based flow control (e.g., a thread limit of 2 effectively behaves as a limit of 1).

Root Cause

The current pointcut @annotation(com.alibaba.csp.sentinel.annotation.SentinelResource) does not specify a join point kind. In Spring AOP (proxy-based), this only matches execution join points since that's all Spring AOP supports. However, in native AspectJ, @annotation matches multiple join point kinds including both call and execution, causing the advice to trigger twice per method invocation.

Fix

Changed the pointcut from:

@Pointcut("@annotation(com.alibaba.csp.sentinel.annotation.SentinelResource)")

to:

@Pointcut("execution(* *(..)) && @annotation(com.alibaba.csp.sentinel.annotation.SentinelResource)")

This explicitly restricts matching to execution join points only, which:

• Has no effect on Spring AOP users (Spring AOP already only supports execution)
• Fixes the double-trigger issue for native AspectJ users
• Makes the pointcut intent explicit and unambiguous

Tests

All 16 existing tests in sentinel-annotation-aspectj pass, including SentinelAnnotationIntegrationTest which validates the annotation-based flow control with Spring AOP.

Impact

Only affects SentinelResourceAspect.java pointcut expression. No behavioral change for Spring AOP users. Fixes thread counting accuracy for native AspectJ users.

Fixes #3597