feat: optimized SolutionHandler and boolean predication support, with…

[pluveto]

This PR refactors the rulog_vm module to improve flexibility, modularity, and testability. Key changes include a more idiomatic Environment struct, the introduction of a SolutionHandler trait for query result processing, and expanded test coverage.

Key Changes

1. Environment Refactor

   • Replaced new() with Default.
   • Added an extend method to facilitate environment extension.

2. SolutionHandler Trait

   • Added the SolutionHandler trait for custom solution handling during query evaluation.
   • Introduced PrintSolutionHandler as a default solution handler.

3. Interpreter Changes

   • Replaced the on_solution callback with SolutionHandler.
   • Updated eval to accept a SolutionHandler for query result processing.

4. Improved QuerySolver

   • Enhanced query resolution logic, including better handling of direct matches between goal and clause.

Breaking Changes

• The on_solution callback in Interpreter is removed. Custom solution handling is now done via the SolutionHandler trait.

Tests

• Added tests for unification with nested structures, lists, and recursive terms.
• Enhanced interpreter tests to verify custom solution handling.