Proposed changes

This patch mainly do the following refactors:

• Use int64_t instead of int32_t for 'version' in DeleteHandler
• Move some comments from .cpp to .h file, add some new comments in .h files, and also remove some meaningless comments
• Use switch...case... instead of multiple if..else.. for DeleteConditionHandler::is_condition_value_valid
• Use range loop to simplify code
• Reduce some compare operations in Cond::del_eval
• Improve some branch predictions in Reader
• Fix and improve some unit tests

Compare with #4925 , this patch fix two bugs:

• Initialize '_collect_iter' which missing initialized when resolve conflict
• Make DeleteHandler and Conditions not copiable and not assignable to avoid double free

Types of changes

What types of changes does your code introduce to Doris?
Put an x in the boxes that apply

• [] Bugfix (non-breaking change which fixes an issue)
• [] New feature (non-breaking change which adds functionality)
• [] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [] Documentation Update (if none of the other choices apply)
• Code refactor (Modify the code structure, format the code, etc...)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• [] I have create an issue on (Fix #ISSUE), and have described the bug/feature there in detail
• Compiling and unit tests pass locally with my changes
• [] I have added tests that prove my fix is effective or that my feature works
• [] If this change need a document change, I have updated the document
• [] Any dependent changes have been merged