refactor: external getFieldFromLine do not need to use strings.ToLower

[huby2358]

What type of PR is this?

• [ ] API-change
• [ ] BUG
• [ ] Improvement
• [ ] Documentation
• [ ] Feature
• [ ] Test and CI
• [x] Code Refactoring

Which issue(s) this PR fixes:

issue # https://github.com/matrixorigin/matrixone/issues/19965

What this PR does / why we need it:

cherry-pick param.Attrs里面用全小写的列名，后面使用的时候不需要再对每个filed都调用strings.ToLower(colname)