Add caching: the Spring cache abstraction, keys, eviction timing and the self-invocation trap

A Spring Boot 4.1.1 module whose test suite is the evidence for the article: 20 tests
producing 22 transcripts under docs/output/, plus 12 documentation chapters.

Findings the build pins:
- @EnableCaching has no exposeProxy attribute; the widely-copied
  @EnableCaching(exposeProxy = true) does not compile.
- Two methods sharing a cache name and an argument type share a key space, and one
  silently serves the other's answers.
- The documented cache-provider detection order does not match CacheType's enum
  order in 4.1.1: COUCHBASE before INFINISPAN, and CACHE2K before CAFFEINE.
- beforeInvocation = true is NOT deferred by TransactionAwareCacheManagerProxy on
  7.0.9 - doEvict picks evictIfPresent, which the decorator does not intercept.
- Four of five invalid declarations start a clean context and throw at the first call.
- Caffeine on the classpath silently displaces the simple provider.

caching/src/main/resources/application.yml

@@ -0,0 +1,26 @@
+spring:
+  application:
+    name: caching
+  jpa:
+    hibernate:
+      ddl-auto: create-drop
+    open-in-view: false
+    properties:
+      hibernate:
+        cache:
+          # Explicit: this module is about the *application* cache, not Hibernate's L2.
+          # See docs/09-versus-hibernate-l2.md for what the difference actually buys you.
+          use_second_level_cache: false
+  sql:
+    init:
+      mode: never
+
+management:
+  endpoints:
+    web:
+      exposure:
+        include: caches,metrics,health
+
+logging:
+  level:
+    org.springframework.cache: INFO