fix: deepcopy should copy same table exactly only once

[nic-6443]

Description

The current deepcopy, when it finds that the original table has already been copied, will directly use the original table. This causes the copied table and the original table to share one table, which does not conform to the semantics of deepcopy. After fixing, the same table will be copied only once by default, we also allow specifying special fields to use shallow copy because, for the health checker module, we need to mount the checker corresponding to the upstream into the original route table so that old checker objects can be released when routes are updated or deleted.

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)