Make MethodUtils CACHE_METHODS volatile (1.X)

[rootvector2]

Port of #414 to the 1.X branch.

setCacheMethods writes CACHE_METHODS under the class monitor but getCachedMethod and cacheMethod read it lock-free on the method-lookup path, so a runtime setCacheMethods(false) may never be observed by other threads and they keep populating and reading the shared static cache; marking the field volatile restores cross-thread visibility while writes stay synchronized so the flag flip and clearCache() remain atomic.

Same caveat as #414: a memory-visibility fix has no deterministic unit test, so none is added. mvn test -Dtest=MethodUtilsTest is green. The full default goal hits one failure in LocaleBeanificationTest.testContextClassloaderIndependence on my machine, but it fails identically on unmodified 1.X and passes standalone, so it is pre-existing and unrelated to this change.

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