feat(vm): Basic Functions

[davydog187]

This implements basic functions without closures. Does not complete Phase 5 yet

• Phase 0: Arithmetic operations and single return
• Phase 1: Local variables with register assignment
• Phase 2: Global variables (get_global, set_global)
• Phase 3: Conditionals (if/elseif/else, and/or short-circuit)
• Phase 4: Loops (while, repeat, numeric for)
• Phase 5: Functions, closures, and upvalues
• Phase 6: Tables and method calls
• Phase 7: Native function calls (Lua→Elixir calling convention)
• Phase 8: Generic for, varargs, and multiple returns
• Phase 9: String concatenation and bitwise operations
• Phase 10: Value encoding/decoding (Lua.VM.Value)
• Phase 11: deflua integration (reimplement lib/lua.ex against VM.State)
• Phase 12: Peephole optimizer
• Phase 13: Remove Luerl dependency