Add resilience4j-circuit-breaker: Resilience4j 2.4.0 vs Spring Framework 7 core, on Boot 4.1

Companion module for the rewritten post 'Resilience4j Circuit Breaker in Spring Boot 4.1:
What It's Still For', reworked around Framework 7 now shipping @Retryable/@ConcurrencyLimit
in core. Covers what's still Resilience4j's job (circuit breaker, rate limiter, bulkhead's
bounded wait, fallback methods, Actuator/Micrometer metrics), the off-by-one between
maxAttempts and maxRetries, and two Boot-4.1 build breaks: spring-boot-starter-aop no longer
exists (renamed to spring-boot-starter-aspectj, proven with Maven Central metadata and the
renamed starter's own POM -- see resilience/docs/08-starter-aop-renamed-to-starter-aspectj.md
in this same repo), and the resulting fix uses that renamed starter directly rather than
assembling spring-aop + aspectjweaver by hand. Kept as its own module rather than a new
top-level repository, alongside the existing resilience/ module for the sibling Framework-7
post.

resilience4j-circuit-breaker/docs/output/03b-retryable-no-memory.txt

@@ -0,0 +1,12 @@
+@Retryable against a permanently-dead downstream: two consecutive calls, no shared state
+========================================================================================
+-- Call 1: pay("order-A") --
+threw FlakyDownstream.DownstreamUnavailableException after exhausting retries
+downstream calls so far: 4  (1 initial attempt + 3 retries = 4 expected)
+
+-- Call 2: pay("order-B"), immediately after Call 1 exhausted its retries --
+downstream calls so far: 8  (another 4 attempts, not fast-failed)
+
+Contrast with docs/output/01-circuitbreaker-trip.txt: there, calls 7-9 after the trip
+added ZERO downstream calls. Here, call 2 pays the same 4-attempt cost as call 1.
+@Retryable has no OPEN state -- it cannot tell you 'this dependency is currently down'.