kv/kvserver: TestFlowControlRangeSplitMerge failed

kv/kvserver.TestFlowControlRangeSplitMerge [failed](https://mesolite.cluster.engflow.com/invocations/default/97cb1e5c-c246-4591-a2b5-29877e5e94cb?testReportRun=2&testReportShard=47&testReportAttempt=1#targets-Ly9wa2cva3Yva3ZzZXJ2ZXI6a3ZzZXJ2ZXJfdGVzdA==) on release-24.3 @ [0fabcb8b0e211756bd5f809cf744d743bc05501d](https://github.com/cockroachdb/cockroach/commits/0fabcb8b0e211756bd5f809cf744d743bc05501d):

```
=== RUN TestFlowControlRangeSplitMerge
test_log_scope.go:165: test logs captured to: outputs.zip/logTestFlowControlRangeSplitMerge3513173818
test_log_scope.go:76: use -show-logs to present logs inline
datadriven.go:144:
/mnt/engflow/worker/work/0/exec/bazel-out/k8-fastbuild/bin/pkg/kv/kvserver/kvserver_test_/kvserver_test.runfiles/com_github_cockroachdb_cockroach/pkg/kv/kvserver/testdata/flow_control_integration/split_merge:1:

output didn't match expected:
@@ -61,15 +61,15 @@
WHERE name LIKE '%kvadmission%tokens%'
ORDER BY name ASC;

kvadmission.flow_controller.elastic_tokens_available | 24 MiB
kvadmission.flow_controller.elastic_tokens_deducted | 30 MiB
- kvadmission.flow_controller.elastic_tokens_returned | 30 MiB
+ kvadmission.flow_controller.elastic_tokens_returned | 26 MiB
kvadmission.flow_controller.elastic_tokens_unaccounted | 0 B
kvadmission.flow_controller.regular_tokens_available | 48 MiB
kvadmission.flow_controller.regular_tokens_deducted | 30 MiB
- kvadmission.flow_controller.regular_tokens_returned | 30 MiB
+ kvadmission.flow_controller.regular_tokens_returned | 26 MiB
kvadmission.flow_controller.regular_tokens_unaccounted | 0 B


-- Observe only the merged replica with its own three streams.
SELECT range_id, count(*) AS streams
panic.go:626: -- test log scope end --
test logs left over in: outputs.zip/logTestFlowControlRangeSplitMerge3513173818
--- FAIL: TestFlowControlRangeSplitMerge (2.40s)
```

Parameters:
- attempt=1
- deadlock=true
- run=2
- shard=47
Help

See also: [How To Investigate a Go Test Failure \(internal\)](https://cockroachlabs.atlassian.net/l/c/HgfXfJgM)

/cc @cockroachlabs/kv-triage

[This test on roachdash](https://roachdash.crdb.dev/?filter=status:open%20t:.*TestFlowControlRangeSplitMerge.*&sort=title+created&display=lastcommented+project) | [Improve this report!](https://github.com/cockroachdb/cockroach/tree/master/pkg/cmd/bazci/githubpost/issues)

Jira issue: CRDB-66285

Start with TestFlowControlRangeSplitMerge and the data-driven case in pkg/kv/kvserver/testdata/flow_control_integration/split_merge. Reproduce the failure on release-24.3 and compare the token metrics in the actual output with the expected values. Done means identifying why the returned-token counts differ and confirming the test's expected result.

Written by the indexing model from the issue text.