feat: type-safe pattern matching

[thetayloredman]

This PR implements type-safety and inference for match statements.

Closes #802

• "cases" syntax for matches
  • redundancy check
• "when-chaining" syntax for matchers
  • redundancy check
  • fix autocomplete
  • Properly handle type validation errors
• "unrestricted matching" (match())
• "restricted matching" (match.only<T>())
  • Exhaustiveness checking
    • Properly handle constraints
• Explicit finalization
• Runtime impl with an ordered union of morphs
• .or methods
  • Implicit finalization
  • .default
    • Properly infer parameter as remaining cases in a match.only
    • With a non-function value, .default(x) behaves as .default(_ => x)
  • .orThrow
• Tests
• Run benchmarks
• Handle non-is-narrowed cases
  • Regex literals
  • predicates
• Bugs:
  • Constraints are not distilled in cases notation