fix(vm): return terse error value for ArgumentError at protected-call boundary

[davydog187]

Summary

• Lua.VM.ProtectedCall.error_value/1 had no clause for Lua.VM.ArgumentError, so it fell through to Exception.message/1 — embedding ANSI codes and the at <source>:<line>: header in the reason returned by Lua.call_function/3 and pcall/xpcall. PR fix(vm): return terse Lua error value from call_function, not terminal render (#336) #337 only fixed the :value-bearing exceptions (RuntimeError, TypeError, AssertionError); ArgumentError builds its message from individual fields and has no :value slot.
• Promote ArgumentError.build_base/5 to a public raw_message/1, and add an ArgumentError clause to error_value/1 that returns it.
• Regression tests for both protected-call boundaries (call_function/3 and pcall), plus tests pinning call_function!/3's structured-exception passthrough.

Fixes #342.

Repro (before)

chunk = ~LUA"""
function foo()
  for i in pairs("asdf") do
    print(i)
  end
end
"""c
{_, lua} = Lua.eval!(chunk)
Lua.call_function(lua, [:foo], [])
# {:error,
#  "\e[2mat -no-source-:\e[0m\n\n  bad argument #1 to 'pairs' (table expected, got string)",
#  #Lua<>}

After

call_function/3 returns the §6.1-faithful terse string (matching pcall's contract):

Lua.call_function(lua, [:foo], [])
# {:error, "bad argument #1 to 'pairs' (table expected, got string)", #Lua<>}

call_function!/3 is the escape hatch for Elixir callers who want the structured exception — it raises Lua.RuntimeException whose :original field carries the underlying VM exception verbatim, so you can pattern-match on it:

try do
  Lua.call_function!(lua, [:foo], [])
rescue
  e in Lua.RuntimeException ->
    case e.original do
      %Lua.VM.ArgumentError{function_name: fn_name, arg_num: n, expected: ex, got: g} ->
        # programmatic dispatch on the structured fields
        ...

      %Lua.VM.RuntimeError{value: v} ->
        # whatever Lua code passed to error()
        ...

      %Lua.VM.TypeError{error_kind: kind} ->
        # :call_nil, :index_non_table, :arith_non_number, etc.
        ...
    end
end

Test plan

• mix test test/lua/call_function_error_value_test.exs (14 cases, +6: ArgumentError regression, ANSI-on variant, and 3 cases pinning call_function!/3's .original contract for ArgumentError/RuntimeError/TypeError)
• mix test test/lua/vm/pcall_error_value_test.exs (+2 cases, one per engine)
• mix test — full suite green (2256+ passed, 19 skipped)
• iex repro from Lua.call_function/3 expected to return Lua.RuntimeException instead of string with ANSI codes #342 returns terse one-line string with no ANSI / no header / no newlines
• mix docs --warnings-as-errors clean
• mix format clean