Optimize ZooKeeper read requests and remove redundant checks

[GGraziadei]

What is the purpose of the change

Refactoring ZooKeeper reads to optimize request volume. Removed unnecessary .exists() calls by handling missing nodes reactively. More details in the linked issue.

Proposed reading pattern

GIVEN path, wantWatch:
      result <- READ path (requesting a watch if wantWatch)  // request #1

      if result is present:
          return result.value   // watch already set if requested
      else:  // node is absent (e.g. `NoNodeException`)
          if wantWatch:
              WATCH path  // request #2, only here
          return EMPTY
      on any other error:
          FAIL 

How was the change tested

• Unit tests
• Added new test cases for node delete-delete conflicts and gestVersion

In the context of #8712

[reiabreu]

There is no test case that does: getData(path, watch=true) on a missing node, then creates the node, and verifies the callback was triggered,
What do you thinking about adding it?

[GGraziadei]

Thank you! I've committed the missing test case.
This test is crucial for preventing regressions. It verifies that if a getData call to zk fails with watched clause enabled, the fallback mechanism successfully registers the watcher manually (calling the method existsNode).

[reiabreu]

Thanks for this contribution @GGraziadei