feat(phase-17): 64-bit integer overflow wrapping and FuncDecl local assignment

[davydog187]

Summary

Critical fixes for Lua 5.3 integer semantics and function declaration behavior.

64-bit Integer Overflow Wrapping ⭐

All integer operations now wrap to signed 64-bit per Lua 5.3 spec:

• Bitwise operations: <<, >>, &, |, ~, ^ wrap to signed 64-bit
• Arithmetic operations: +, -, *, //, %, unary - wrap for integer operands
• Added to_signed_int64/1 helper for proper IEEE 754 compliance
• maxint + 1 now correctly equals minint
• 1 << 63 now correctly equals minint (not overflow to big integer)

FuncDecl Local Assignment ⭐

Fixed function f() syntax to properly update local variables:

• function f() now correctly updates local f when one exists in scope
• Scope resolution marks assignment target in var_map at declaration time
• Prevents future locals from incorrectly affecting earlier code during codegen
• Fixes common Lua pattern where local f = function()... is followed by function f()

Example fixed pattern:

local f = function(x) return "first" end
-- Later redefine f
function f(x) return "second" end
-- f now correctly refers to "second"

Implementation Details

Integer Wrapping:

• to_signed_int64/1 masks to 64 bits then converts to signed range
• Applied to all bitwise ops: band, bor, bxor, bnot, bsl, bsr
• Applied to integer arithmetic: safe_add, safe_subtract, safe_multiply, safe_negate, lua_idiv, safe_modulo
• Float operations remain IEEE 754 (no wrapping)

FuncDecl Fix:

• Scope resolution checks if local exists at FuncDecl position
• Stores target as {:func_decl_target, decl} in var_map
• Codegen uses this marker instead of checking ctx.scope.locals (which contains all function-scope locals)

Test Status

• Unit tests: 1,273 passing, 0 failures ✅
• No regressions: All existing tests continue to pass
• Enables progress: constructs.lua now progresses past line 160 (was failing at line 20)

Dependencies

Depends on #141 (vararg and scope fixes).

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