Resolve all TODOs and stubs in codebase

[hyperpolymath]

This commit implements numerous TODO items across the core compiler:

lib/types.ml:

• Add pretty printing for types, rows, effects, kinds, predicates
• Implement type substitution (subst_ty)
• Add free type variable collection (free_tyvars)
• Add occurs check helper
• Implement type-level nat normalization and equality

lib/typecheck.ml:

• Implement type variable lookup via symbol table
• Add AST to internal predicate/nat conversion
• Implement dependent arrow type conversion
• Add handler effect checking
• Implement try/catch type checking
• Add row restriction for records
• Implement constructor pattern binding
• Add type/effect/trait/impl declaration checking

lib/unify.ml:

• Add predicate compatibility checking
• Implement alpha-equivalence for forall types
• Add normalized nat comparison
• Implement set-based effect unification

lib/symbol.ml:

• Add qualified path lookups
• Implement visibility checking
• Add import registration
• Add effect operation lookups

lib/resolve.ml:

• Implement unsafe operation resolution
• Add impl block resolution
• Implement import resolution

lib/borrow.ml:

• Add move site tracking in error messages
• Implement proper if-then-else branch state handling

lib/quantity.ml:

• Implement proper branch handling for if expressions

justfile:

• Implement release workflow with version update and tagging