Document combining @Retryable with proxy-based features

[jhan0121]

Document the semantics of combining @Retryable with other proxy-based annotations (@Transactional, @Cacheable, and @Async), addressing the advice chain ordering that determines retry behavior.

Changes

Tests

• Add withCacheableAnnotation() to RetryInterceptorTests verifying that retry is applied outside the cache interceptor (Retry OUTER -> Cache INNER).
• Add RetryableTransactionTests in spring-tx verifying that each retry attempt starts a fresh transaction (Retry OUTER -> TX INNER). Placed in spring-tx to avoid a circular module dependency.

Javadoc

• Add a paragraph to @Retryable documenting the proxy interaction semantics and pointing to EnableResilientMethods#order() and EnableAsync#order() for customizing the order relative to @Async (the order relative to @Transactional/@Cacheable is fixed).

Reference documentation

• Add a "Combining @Retryable with Other Proxy-Based Features" section to resilience.adoc, covering the default advice chain order for each combination, and advice order customization between @Retryable and @Async via @EnableResilientMethods(order)/@EnableAsync(order) (this customization does not apply to @Transactional/@Cacheable,
  whose shared InfrastructureAdvisorAutoProxyCreator always runs first).
• Add cross-reference TIP blocks to the @Transactional and @Async reference sections pointing to the new combining section.

Spring Boot compatibility

Verified with a dedicated validation repository (https://github.com/jhan0121/spring-resilience-boot-validation) that the advice chain order is consistent across all Spring Boot 4.x GA releases (4.0.0 through 4.1.0) under auto-configuration:

Scenario	Order	Result
@Retryable + @Transactional	Retry OUTER → TX INNER	PASS
@Retryable + @Cacheable	Retry OUTER → Cache INNER	PASS
@Retryable + @Async	Async OUTER → Retry INNER	PASS

Closes gh-35584