Optimize single-node master/replica reads

[Sean-Kenneth-Doherty]

Summary

• return the selected connection directly when ReadFrom resolves to exactly one node
• avoid building/subscribing a Reactor Flux chain on the single-node hot path
• add a unit test that verifies the single-node path bypasses the old open-filter path

Fixes #3744.

Verification

• ~/.local/share/mise/installs/maven/3.9.11/apache-maven-3.9.11/bin/mvn -Dtest=io.lettuce.core.masterreplica.MasterReplicaConnectionProviderUnitTests test
  • Tests run: 2, Failures: 0, Errors: 0, Skipped: 0

Note: mvn via the mise shim was not configured in this shell, so I used the installed Maven 3.9.11 binary directly.

---

Note

Low Risk
Low risk: small performance-oriented change to the READ connection selection path plus a unit test; behavior only differs by skipping the open-filter/Flux pipeline when exactly one node is selected.

Overview
Optimizes master/replica READ connection selection by short-circuiting to a direct connection when ReadFrom resolves to exactly one node, avoiding construction/subscription of the Reactor Flux chain.

Updates the selection logic to only use the order-sensitive isOpen filtering path for multi-node selections, and adds a unit test ensuring the single-node path returns the connection directly without calling isOpen().

^{Reviewed by Cursor Bugbot for commit 7a4a162. Bugbot is set up for automated code reviews on this repo. Configure here.}

[Sean-Kenneth-Doherty]

Local validation on head 7a4a1621d4cf8cd57b795f85edad7e1080c13324:

• inspected the patch; it only touches MasterReplicaConnectionProvider and the corresponding unit test
• the fast path returns the sole selected node directly before building/filtering the Reactor connection sequence
• the new unit test covers ReadFrom.ANY with a single selected node and verifies the returned connection is the node connection while isOpen() is not called
• mise x [email protected] -- mvn -Dtest=MasterReplicaConnectionProviderUnitTests test -> build success; 2 tests run, 0 failures, 0 errors
• git diff --check origin/main...HEAD -> clean

Hosted PR checks currently show no failures; only Cursor Bugbot and Jit Security are configured on this PR.

[a-TODO-rov]

Thanks @Sean-Kenneth-Doherty
@atakavci do you think we can merge this ?
It looks good to me.