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.

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

Additional context

N/A.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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

Additional details and impacted files

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

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