store/copr: partly revert pr/35975, do it correctly this time (#55196)

[ti-chi-bot]

This is an automated cherry-pick of #55196

What problem does this PR solve?

Issue Number: close #54969

Problem Summary:

What changed and how does it work?

#55155 try to revert pr/35975 but not clean, coupling with #41500 and bring bugs. PartitionNum is 1 even on non-partitioned table.

Do it correctly in this PR.
The new behaviour now:

• The 'select ... where ... order by ...' query will not reduce distsql concurrency to 2 (change)
• The simple 'select ... limit N' query, when N < 10000 , distsql concurrency is set to 1 (keep the behavior no change)
  • The same 'select ... limit N' query, on partitioned table, distsql concurrency is set to partition number (keep the behavior no change)

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

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Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/unit-test	feafbd4	link	true	/test unit-test
idc-jenkins-ci-tidb/check_dev_2	feafbd4	link	true	/test check-dev2
idc-jenkins-ci-tidb/build	feafbd4	link	true	/test build
idc-jenkins-ci-tidb/mysql-test	feafbd4	link	true	/test mysql-test
idc-jenkins-ci-tidb/check_dev	feafbd4	link	true	/test check-dev

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[ti-chi-bot]

PR needs rebase.

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