[FLINK-40150][tests] De-parameterize rescale-history-enabled RescaleTimelineITCase tests

[MartijnVisser]

What is the purpose of the change

FLINK-40150. The six terminated-reason tests in RescaleTimelineITCase only assert
when rescale history is enabled, yet ran as @TestTemplate: on the disabled-history
parameter each paid for a MiniCluster startup before assumeThat aborted, and three
rebuilt the cluster on top of that. This eliminates those wasted startups.

The jira was scoped to the 3 assume+rebuild methods; this broadens it to all 6
assume-guarded methods, since the assume+enabled-only pattern applies to the same set.

Brief change log

• Extract shared fixture and helpers into a new abstract RescaleTimelineITCaseBase.
• Move the 6 enabled-only tests to a new non-parameterized RescaleTimelineHistoryEnabledITCase;
  each starts one cluster per test with the configuration it needs (no throwaway rebuild),
  and the assumeThat guards are dropped.
• RescaleTimelineITCase keeps the 8 genuinely per-parameter cases (and the 2 @Disabled).

No production code and no behavior change; all timeouts and configs are preserved.

Verifying this change

This change is a test-only refactor covered by existing tests:
RescaleTimelineITCase (16 executed over 2 parameters, 2 disabled) and
RescaleTimelineHistoryEnabledITCase (6, each run once) both pass.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

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Was generative AI tooling used to co-author this PR?

• Yes (Claude Code, Claude Opus 4.8)

Generated-by: Claude Code (Claude Opus 4.8)

[flinkbot]

CI report:

• a09f08d Azure: FAILURE

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[spuru9]

The test failure is unrelated. But you may rerun for green CI.