feat: added TwoSat solutions with Tests, also updated Directory.md (#6756)

* feat: added TwoSat solutions and Tests and also updated Directory.md

* added reference urls to the article related to the 2-SAT

* Fix generic type warnings in TwoSat.java

* maven build fix: added rawtypes in SuppressWarnings

* fixed  checkstyle error

* fix: Sorted import order

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Co-authored-by: a <alexanderklmn@gmail.com>