*: fix panic when reusing OptimisticTxnContextProvider

[lcwangchao]

What problem does this PR solve?

Issue Number: close #38951

Problem Summary:

To reduce space allocation, we used to reserve OptimisticTxnContextProvider to txnManager that cause the old and new OptimisticTxnContextProvider be the same. After ResetForNewTxn , the old provider's state will be corrputed.

It is triggered when new MDL codes merged, see: #38926 (comment)

What is changed and how it works?

Reserve two OptimisticTxnContextProvider and make the old and the new one not the same.

Check List

• No code

Release note

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None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• hawkingrei
• xhebox

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[lcwangchao]

/check-issue-triage-complete

[hawkingrei]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: d45eacc

[sre-bot]

TiDB MergeCI notify

🔴 Bad News! New failing [1] after this pr merged.
These new failed integration tests seem to be caused by the current PR, please try to fix these new failed integration tests, thanks!

CI Name	Result	Duration	Compare with Parent commit
idc-jenkins-ci-tidb/common-test	🟥 failed 1, success 10, total 11	9 min 9 sec	New failing
idc-jenkins-ci-tidb/integration-ddl-test	🔴 failed 3, success 3, total 6	43 min	Existing failure
idc-jenkins-ci/integration-cdc-test	🔴 failed 1, success 38, total 39	18 min	Existing failure
idc-jenkins-ci-tidb/mybatis-test	🔴 failed 1, success 0, total 1	10 min	Existing failure
idc-jenkins-ci-tidb/integration-common-test	🟢 all 17 tests passed	13 min	Existing passed
idc-jenkins-ci-tidb/tics-test	🟢 all 1 tests passed	6 min 20 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2	🟢 all 28 tests passed	5 min 19 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1	🟢 all 26 tests passed	4 min 49 sec	Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test	🟢 all 1 tests passed	2 min 29 sec	Existing passed
idc-jenkins-ci-tidb/plugin-test	🟢 build success, plugin test success	4min	Existing passed