* refactor code, move appendFetchVertexPlan() to MatchSolver

* add implementation for match exactly 0 step

* add simple tests and fix typo

* add implementation for match 0..n step

* fix left node expansion

* add string vid tests

* add int vid tests

* refactor code

* remove redundant code

* add overloaded method appendFetchVertexPlan()

* add more tests

* update int vid test

* address comments, fix passThrough()

* fix conflicts

Co-authored-by: Yee <2520865+yixinglu@users.noreply.github.com>