kv (ticdc): Improve the codebase of kvClient. (#10585)

[ti-chi-bot]

This is an automated cherry-pick of #10585

What problem does this PR solve?

Issue Number: ref #10584

What is changed and how it works?

• Move stream related filed into eventFeedStream struct to make the code more clear.
• Reduce a lock usage by make sure the storeStreamsCache can only be accessed in one goroutine.

Check List

Tests

• Manual test (add detailed scripts or steps below)

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

None

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[ti-chi-bot]

@ti-chi-bot: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
jenkins-ticdc/verify	541a7ed	link	true	/test verify
pull-dm-integration-test	541a7ed	link	true	/test dm-integration-test
pull-cdc-integration-mysql-test	541a7ed	link	true	/test cdc-integration-mysql-test
pull-cdc-integration-storage-test	541a7ed	link	true	/test cdc-integration-storage-test
pull-cdc-integration-kafka-test	541a7ed	link	true	/test cdc-integration-kafka-test
pull-dm-compatibility-test	541a7ed	link	true	/test dm-compatibility-test

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[asddongmen]

This cherry-pick is contained in #10571.

[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by triage owners.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick:

1. It must be approved by the approvers firstly.
2. AFTER it has been approved by approvers, please wait for the cherry-pick merging approval from triage owners.

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