Replace parser gem with prism for Witchcraft AST parsing

[t6n]

Description

Motivation

The parser gem only supports Ruby syntax up to version 3.3 and will not receive updates for Ruby 3.4+. Starting with Ruby 3.4, Prism is the
official parser built into Ruby itself and is the recommended tool for all AST-related operations going forward.

This change future-proofs the Witchcraft feature by switching to Prism before parser becomes incompatible with newer Ruby versions.

Changes

• Replace require 'parser/current' with require 'prism'
• Use Prism::Translation::ParserCurrent.parse instead of Parser::CurrentRuby.parse
• Update check_requirements! to check for the Prism constant instead of Parser

Technical Notes

Prism provides a translation layer (Prism::Translation::ParserCurrent) that produces Parser::AST::Node objects identical to those from the parser
gem. This means:

• All existing AST transformation methods continue to work unchanged
• unparser remains fully compatible since it receives the same node types
• No changes required to the AST manipulation logic (replace_lvar, replace_send, replace_self, etc.)

Dependencies

The Witchcraft feature now requires prism instead of parser as a direct dependency. Note that unparser still has parser as a transitive
dependency for its AST node classes, but this is handled internally and does not affect Chewy's public API.