Support FromSlice and FromMap helpers in itx

[BooleanCat]

Please provide a brief description of the change.

Using itx.From(slices.Values(slice)) will be a fairly common pattern so this is to make that a bit less verbose with itx.FromSlice(slice) (and same for FromMap).

Which issue does this change relate to?

None.

Contribution checklist.

• [x] I have read and understood the CONTRIBUTING guidelines
• [x] All commits in my PR conform to the commit hygiene section
• [x] I have added relevant tests
• [x] I have not added any dependencies

Additional context

N/A.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (cf660a4) to head (42b7a4d).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #127 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 32 32 Lines 434 438 +4 ========================================= + Hits 434 438 +4 ```

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