refactor(it): move SeqToSeq2 from map.go to seq.go

[samber]

Summary

• Moves SeqToSeq2 from it/map.go to it/seq.go (correct file — it operates on sequences, not maps)
• Moves test and example from map_test.go/map_example_test.go to seq_test.go/seq_example_test.go
• Adds maps import to seq_test.go and seq_example_test.go
• Adds doc page docs/data/it-seqtoseq2.md
• Improves doc comment to clarify the index starts at 0 and increments by 1

[codecov]

Codecov Report

❌ Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.60%. Comparing base (79e0b08) to head (66c1205).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
it/seq.go	71.42%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #898      +/-   ##
==========================================
+ Coverage   92.58%   92.60%   +0.01%     
==========================================
  Files          32       32              
  Lines        5082     5082              
==========================================
+ Hits         4705     4706       +1     
+ Misses        274      273       -1     
  Partials      103      103              

Flag	Coverage Δ
unittests	92.60% <71.42%> (+0.01%)	⬆️

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[Copilot]

Pull request overview

This PR relocates the SeqToSeq2 iterator helper to the more appropriate it/seq.go module, and updates associated tests/examples and documentation accordingly.

Changes:

• Moved SeqToSeq2 implementation from it/map.go to it/seq.go and clarified its doc comment (index starts at 0 and increments by 1).
• Moved SeqToSeq2 test and example from map-focused test files to sequence-focused test files (adding maps imports where needed).
• Added a new docs page for SeqToSeq2 under docs/data.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
it/seq.go	Adds SeqToSeq2 implementation and doc comment in the sequence helpers file.
it/seq_test.go	Adds TestSeqToSeq2 and imports maps for maps.Collect.
it/seq_example_test.go	Adds ExampleSeqToSeq2 and imports maps.
it/map.go	Removes SeqToSeq2 from the map helpers file.
it/map_test.go	Removes TestSeqToSeq2 from map tests.
it/map_example_test.go	Removes ExampleSeqToSeq2 from map examples.
docs/data/it-seqtoseq2.md	Adds a new documentation page for SeqToSeq2.

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