feat(phase-17): Vararg expansion, scope fixes, and suite triage

[davydog187]

Summary

Major improvements for Lua 5.3 compliance:

Multi-Return & Vararg Expansion

• Implement multi-return value expansion across call arguments, table constructors, and return statements
• Vararg expansion in local/regular multi-assignment (local a, b, c = ...)
• Vararg support in function calls (f(a, b, ...)) and table constructors ({a, b, ...})
• Main chunk marked as vararg per Lua 5.3 spec (enables load() varargs)

Scope & Register Management

• Fix for-loop register allocation: reserve 3 registers for internal counter/limit/step
• Fix upvalue nesting: rewrite find_upvalue as ensure_upvalue for correct 3+ level upvalue chains
• Move open_upvalues to State struct for proper persistence through loops
• Temp register recycling in gen_block to prevent register overflow
• max_registers uses peak next_reg from codegen (not just scope locals)

Compiler Fixes

• Floor division/modulo use Lua 5.3 floor semantics
• FuncDecl dotted names: emit closure instructions, use gen_var_by_name for local table lookups
• Float literal parsing: .0, 0., 2.E-1, hex float literals now valid
• Local function redefinition scoping fixes

Standard Library

• string.packsize implementation
• table.unpack nil handling
• assert returns all arguments
• _ENV support

Test Status

• Suite tests: 4/29 passing (simple_test.lua, api.lua, code.lua, vararg.lua) - up from 1/29
• Unit tests: 1,273 passing, 0 failures

Breaking Changes

None - all existing tests continue to pass.

🤖 Generated with Claude Code