Pattern matching for more robust syntax verification in Python

[GlowingScrewdriver]

The basis for this was laid in #49, which added a function called verify_shape to verify the shapes of lists.
As of now, verify_shapes is capable of recursively checking the lengths and element types of lists, and is used by gen_set_expr to check the syntax of a set expression.

Such a pattern matching framework calls for a discussion before further development.

We can probably take inspiration from Python's own match statement for pattern matching. The only reason it may not be feasible for our use is that we will have to write match-case statements everywhere, which can get messy unlike one-liner function calls.

[GlowingScrewdriver]

This should also help with issues like #59.

[chsasank]

Inspiration for this is from

1. https://github.com/norvig/paip-lisp/blob/main/docs/chapter5.md
2. https://github.com/norvig/paip-lisp/blob/main/docs/chapter6.md#62-a-pattern-matching-tool
3. https://github.com/norvig/paip-lisp/blob/main/docs/chapter11.md