feat: add IterateColumns method for improved performance

[DengY11]

PR Details

Add rows.IterateColumns(iterateFunc), iterate it with a callback function instead create a huge []string.And that will enhance memory performance

Related Issue

close #2191

Example:

err := rows.IterateColumns(func(index int, cell string) error {
    fmt.Printf("column %d: %s\n", index, cell)
    return nil
})

How Has This Been Tested

go test

Types of changes

• [ ] Docs change / refactoring / dependency upgrade
• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• [x] My code follows the code style of this project.
• [] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[codecov[bot]]

Codecov Report

:x: Patch coverage is 53.12500% with 30 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 99.14%. Comparing base (5d2ee53) to head (afebad2). :warning: Report is 21 commits behind head on master.

Files with missing lines	Patch %	Lines
rows.go	53.12%	22 Missing and 8 partials :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2196      +/-   ##
==========================================
- Coverage   99.24%   99.14%   -0.10%     
==========================================
  Files          32       32              
  Lines       30562    30626      +64     
==========================================
+ Hits        30331    30365      +34     
- Misses        153      175      +22     
- Partials       78       86       +8     

Flag	Coverage Δ
unittests	99.14% <53.12%> (-0.10%)	:arrow_down:

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[ankisme]

Is this pr still adding? Wish to add the feature