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.

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Note

Low Risk
Low risk behavioral change limited to ReadFrom read selection when it resolves to a single node; it mainly skips Reactor assembly and isOpen filtering, with a unit test covering the new path.

Overview
Optimizes master/replica read connection selection by short-circuiting when ReadFrom resolves to exactly one node, returning that node’s connection directly instead of building a Reactor Flux chain.

This removes the redundant single-node isOpen/fallback logic from the reactive selection path and adds a unit test (shouldUseDirectConnectionForSingleReadSelection) to assert the direct-connection behavior (and that isOpen() is not consulted).

^{Reviewed by Cursor Bugbot for commit a3e582e. 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 maven@3.9.11 -- 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.

[atakavci]

hey, seems pretty good to me.
thank you @Sean-Kenneth-Doherty 🙏