[DNM]: Use Tidwall btree in region cache

[cfzjywxk]

Ref: https://github.com/tikv/client-go/compare/master...zyguan:client-go:exp/use-tidwall-btree

Replace the btree usage to tidwall btree in region cache.

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Once this PR has been reviewed and has the lgtm label, please ask for approval from cfzjywxk, ensuring that each of them provides their approval before proceeding. For more information see the Code Review Process.

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

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment Approvers can cancel approval by writing /approve cancel in a comment