[PR] [AMORO-4462][AMS] Publish overview top-table cache atomically [amoro]

["sivakumar-mahalingam (via GitHub)" <gi...@apache.org>]

sivakumar-mahalingam opened a new pull request, #4463:
URL: https://github.com/apache/amoro/pull/4463

   ## Why are the changes needed?
   
   `OverviewManager` stores the top-table cache in a shared mutable `ArrayList`. The background refresh thread updates this list using separate `clear()` and `addAll()` operations while HTTP request threads may read it.
   
   As a result, a request can observe an empty or inconsistent intermediate cache state during a refresh. The cache should instead publish complete snapshots atomically so readers always receive either the previous snapshot or the newly refreshed snapshot.
   
   Close #4462.
   
   ## Brief change log
   
   - Replace the mutable top-table cache with a volatile immutable snapshot.
   - Build the complete snapshot before publishing it with a single assignment.
   - Return the published immutable snapshot directly to readers.
   - Add a regression test covering snapshot immutability and replacement during refresh.
   
   ## How was this patch tested?
   
   - [x] Added a regression test in `TestOverviewManager` that verifies the snapshot remains stable between refreshes and is replaced after a refresh.
   
   - [x] Screenshots are not applicable because this change does not affect the UI.
   
   - [x] Ran the targeted test locally:
   
     ```shell
     ./mvnw -pl amoro-ams -am -Pskip-dashboard-build \
       -Dtest=TestOverviewManager \
       -Dsurefire.failIfNoSpecifiedTests=false test
     ```
   
     Result: 2 tests passed with no failures, errors, or skips.
   
   - [x] Ran repository validation locally:
   
     ```shell
     ./mvnw validate
     ```
   
     Result: all 33 modules passed Spotless and Checkstyle validation.


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