Fix TiFlash overflow

[shiyuhang0]

What problem does this PR solve?

Reproduce:

create and insert

CREATE TABLE test.t(`a` bigint(20) UNSIGNED NOT NULL)
insert into t values (16717361816800086255)

query from tispark with tiflash returns an error result（negative number）

 spark.conf
        .set("spark.tispark.isolation_read_engines","tiflash")
spark.sql("select * from tidb_catalog.test.t").show()

What is changed and how it works?

TiSpark requests TiFlash using TypeCHBlock encode, but forgets to handle the UNSIGNED scenes when decoded.

this pr shows how to decode it corretly

Check List

Tests

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

Code changes

• Has exported function/method change
• Has exported variable/fields change
• Has interface methods change
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation
• Need to update the tidb-ansible repository
• Need to be included in the release note

[shiyuhang0]

/run-all-tests

[shiyuhang0]

/run-all-tests

[shiyuhang0]

/run-all-tests

[shiyuhang0]

/run-all-tests

[shiyuhang0]

/run-all-tests

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: xuanyu66, zhangyangyu

The full list of commands accepted by this bot can be found here.

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/pingcap/tispark/blob/master/OWNERS)~~ [xuanyu66] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2023-08-01 03:24:55.913210286 +0000 UTC m=+155779.855558814: :ballot_box_with_check: agreed by xuanyu66.
• 2023-08-01 07:01:14.647476771 +0000 UTC m=+168758.589825299: :ballot_box_with_check: agreed by zhangyangyu.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-2.5: #2741.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-3.0: #2742.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-3.1: #2743.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-3.2: #2744.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-2.4: #2745.