GH-5385: Improve performance of MongoStepExecutionDao::getLastStepExecution

[seonwooj0810]

Fixes #5385.

Summary

MongoStepExecutionDao#getLastStepExecution currently fetches all step executions for the job instance into memory, then filters by step name and sorts on (createTime, stepExecutionId) in Java. The single-row contract makes this an O(N) cost that grows with the step-execution history despite the O(1) result.

This PR pushes the step name filter, ordering (createTime DESC, then stepExecutionId DESC) and limit(1) down to MongoDB, mirroring the optimization PR #4798 applied to the JDBC variant. It also removes the existing // TODO optimize the query marker.

The contract StepExecutionDao#getLastStepExecution ("Retrieve the last StepExecution for a given JobInstance ordered by creation time and then id") is preserved.

Changes

• MongoStepExecutionDao#getLastStepExecution: filter (name), sort (createTime DESC, stepExecutionId DESC), and limit(1) are now applied via the Query and resolved by MongoOperations#findOne (which respects Query#getSortObject by delegating to find with limit(1)).
• MongoStepExecutionDaoIntegrationTests: added testGetLastExecutionFiltersByStepName to assert correct filtering when multiple step names share the same job instance, and to assert that a non-existent step name returns null. Existing tests (testSaveAndGetLastExecution, testSaveAndGetLastExecutionWhenSameStartTime) remain unchanged and continue to cover the createTime-then-id ordering contract.

Test plan

• ./mvnw -pl spring-batch-core compile -DskipTests — passes
• ./mvnw -pl spring-batch-core test-compile -DskipTests — passes
• ./mvnw -pl spring-batch-core spring-javaformat:validate — passes
• Mongo integration tests are gated on @Testcontainers(disabledWithoutDocker = true) and could not be executed in my local environment (no Docker daemon access). They are exercised by upstream CI.

Verification done

• (1) PR list searched on 5385: none found at the time of writing.
• (2) Issue thread: no in-flight claim; the reporter mentioned willingness to submit a PR on 2026-04-22 but no PR has materialized in the 36 days since. Treating as stalled per "no follow-up in >21 days." Credit to @config25 for the detailed problem description, current-behavior trace, and direction in the issue body.
• (3) Code-focused change: .java only.
• (4) Verified the pattern still exists on main (// TODO optimize the query + in-memory filter/sort at MongoStepExecutionDao.java:115-147).
• (5) Prior art: PR Improve performance of JdbcStepExecutionDao::getLastStepExecution #4798 (Improve performance of JdbcStepExecutionDao::getLastStepExecution) — same shape of fix on the JDBC side, mirrored here for Mongo.