Add SK and CS locales

[tomaschyly]

What does this PR do?

I have added SK and CS locales

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Maintenance change (non-breaking change such as upgrading a dependency, refactoring, or making a lint fix)
• [x] Documentation update
• [ ] Breaking change (a fix or feature that would cause existing functionality to change)

Checklist

• [x] Wrote additional tests, if needed
• [x] All tests have passed
• [x] I have updated the documentation accordingly, if needed.

[jama5262]

@tomaschyly please add tests for these two locales here locales_test.dart

You can also follow this discussion https://github.com/jama5262/jiffy/discussions/231

[tomaschyly]

@jama5262 I have added tests for these two locales

[tomaschyly]

@jama5262 do you plan to merge this, or is there some issue?

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.12 :tada:

Comparison is base (20cd464) 96.33% compared to head (30b9867) 96.45%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #230 +/- ## ========================================== + Coverage 96.33% 96.45% +0.12% ========================================== Files 34 36 +2 Lines 1554 1610 +56 ========================================== + Hits 1497 1553 +56 Misses 57 57 ``` | [Impacted Files](https://app.codecov.io/gh/jama5262/jiffy/pull/230?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jama+Mohamed) | Coverage Δ | | |---|---|---| | [lib/src/locale/locales/cs\_locale.dart](https://app.codecov.io/gh/jama5262/jiffy/pull/230?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jama+Mohamed#diff-bGliL3NyYy9sb2NhbGUvbG9jYWxlcy9jc19sb2NhbGUuZGFydA==) | `100.00% <100.00%> (ø)` | | | [lib/src/locale/locales/sk\_locale.dart](https://app.codecov.io/gh/jama5262/jiffy/pull/230?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jama+Mohamed#diff-bGliL3NyYy9sb2NhbGUvbG9jYWxlcy9za19sb2NhbGUuZGFydA==) | `100.00% <100.00%> (ø)` | | | [lib/src/locale/supported\_locales.dart](https://app.codecov.io/gh/jama5262/jiffy/pull/230?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jama+Mohamed#diff-bGliL3NyYy9sb2NhbGUvc3VwcG9ydGVkX2xvY2FsZXMuZGFydA==) | `100.00% <100.00%> (ø)` | |

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