refactor: implement Display for Term, add environment methods, and enhance solution handlers

[pluveto]

Summary

This pull request introduces several enhancements and refactors across the project, focusing on improving code readability, functionality, and output handling.

Changes

Cargo.toml

• Updated the workspace resolver to version "2" for improved dependency resolution.

AST Module (rulog_core/src/types/ast.rs)

• Implemented the Display trait for the Term enum to enable formatted string representations of terms.
• This enhancement allows for more readable output when terms are printed.

Environment Module (rulog_vm/src/environment.rs)

• Added is_empty method to check if the environment has no bindings.
• Introduced an iter method to iterate over environment bindings, facilitating better access and manipulation.

Interpreter Module (rulog_vm/src/interpreter.rs)

• Replaced PrintSolutionHandler with ConsoleSolutionHandler for better naming consistency.
• Added WriteSolutionHandler, allowing solutions to be written to any Write implementor.
• The WriteSolutionHandler can now format and print solutions or indicate when no solution is found.