Move find to iter.go

[Rajan-226]

Please provide a brief description of the change.

Move Find to iter.go

Which issue does this change relate to?

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If there is no such issue, consider creating one first. Discussions concerning proposed changes ought to take place in an issue and not in pull requests. Pull requests not associated with an issue are less likely to be merged and more likely to ask for changes.

Contribution checklist.

Replace the space in each box with "X" to check it off.

• [ ] I have read and understood the CONTRIBUTING guidelines
• [ ] My code is formatted (make check)
• [ ] I have run tests (make test)
• [ ] All commits in my PR conform to the commit hygiene section
• [ ] I have added relevant tests
• [ ] I have not added any dependencies

Additional context

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[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (291888d) 100.00% compared to head (d6063ee) 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #54 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 19 18 -1 Lines 382 382 ========================================= Hits 382 382 ``` | [Files Changed](https://app.codecov.io/gh/BooleanCat/go-functional/pull/54?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Tom+Godkin) | Coverage Δ | | |---|---|---| | [iter/iter.go](https://app.codecov.io/gh/BooleanCat/go-functional/pull/54?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Tom+Godkin#diff-aXRlci9pdGVyLmdv) | `100.00% <100.00%> (ø)` | |

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[Rajan-226]

@BooleanCat Please check