Words supporting nft::post

[koniksedy]

This PR:

• Added multiple overloads of the post method in nft.hh to support:
  • Computing reachable states for sets of states and words across different levels.
  • Handling bitmask-based and vector-based level selection for transitions.
  • Providing options for epsilon closure, jump modes, and early stopping via a callback.
• Introduced the JumpMode parameter to is_in_lang, is_in_lang_prefix, is_in_lang_by_levels, and related methods, allowing users to specify how jump transitions are interpreted.