[I] Registry.getRegistryOfClass returns a registry of the wrong class instead of failing [hudi]

["voonhous (via GitHub)" <gi...@apache.org>]

voonhous opened a new issue, #19893:
URL: https://github.com/apache/hudi/issues/19893

   Found while reviewing #19892 (part of #19524).
   
   `Registry.REGISTRY_MAP` (hudi-io, `org.apache.hudi.common.metrics.Registry`) is a JVM-wide static that is never cleared. `SparkHoodieBackedTableMetadataWriter.initRegistry()` interns the metadata registry under the table-name-less key `""::HoodieMetadata`. When metrics are on and executor metrics are off it stores a `LocalRegistry`; when executor metrics are on with a non-INMEMORY reporter it calls `Registry.getRegistryOfClass(..., DistributedRegistry.class)`. On a class mismatch `getRegistryOfClass` only logs "already exists with a different class" and returns the existing `LocalRegistry`, which the caller then hard-casts.
   
   Reproduces at one surefire fork just by ordering two existing tests in one JVM:
   
   ```
   mvn test -am -pl hudi-spark-datasource/hudi-spark -Dspark3.5 -Dscala-2.12 -DskipUTs=true \
     -Dhudi.surefire.forkCount=1 -Dsurefire.runOrder=reversealphabetical \
     -Dtest='TestMetricsReporter,TestMetadataTableWithSparkSQL' ...
   # ClassCastException: LocalRegistry cannot be cast to DistributedRegistry
   ```
   
   The alphabetical order passes, and each class passes alone. Any change to how classes are grouped into JVMs (fork count, new tests, renamed classes) can flip it.
   
   Proposed fix: key the metadata registry per table (or per base path), and have `getRegistryOfClass` replace or throw on a class mismatch rather than return the wrong type. A test-side reset of `REGISTRY_MAP` between classes would hide the symptom but not the production bug.


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