Simplify README examples with type inference

[BooleanCat]

Please provide a brief description of the change.

Use Go 1.21+ type inference to make README easier to read.

Which issue does this change relate to?

https://github.com/BooleanCat/go-functional/issues/44

Contribution checklist.

• [X] I have read and understood the CONTRIBUTING guidelines
• [X] My code is formatted (make check)
• [X] I have run tests (make test)
• [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

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (78df544) 100.00% compared to head (1128651) 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #52 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 19 19 Lines 376 376 ========================================= Hits 376 376 ```

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