GeezerVison

In `@crates/codegen/src/ir.rs`:
- Line 734: Replace the unchecked cast u32::from(info.arg) as i32 with a checked
conversion using i32::try_from(u32::from(info.arg)) and handle the Err case
instead of allowing silent wraparound; specifically, call
instr.stack_effect(i32::try_from(u32::from(info.arg)).expect("OpArg out of i32
range")) or propagate an error if appropriate for your context, and make the
same replacement for the other occurrence noted (the second use of
instr.stack_effect with info.arg).

In `@crates/compiler-core/src/bytecode/instruction.rs`:
- Around line 900-906: The match arm for the opcode BinaryOpInplaceAddUnicode
currently returns 0 pushes which contradicts the IR treatment (pop 2 / push 1)
and causes stack_effect = -2; update the implementation that computes pushes
(e.g., num_pushed or the match in instruction.rs where BinaryOpInplaceAddUnicode
is handled) to return 1 like the other binary ops
(BinaryOpAddFloat/Int/Unicode/Extend/Multiply) so the stack depth calculation
matches the IR semantics.

In `@crates/compiler-core/src/bytecode/instruction.rs`:
- Around line 1396-1435: The From<StackEffect> for i32 impl uses unsafe
unwrap_unchecked on conversions of StackEffect.pushed() and .popped(), which can
UB if values exceed i32::MAX; replace the unsafe block by performing safe
conversions (use i32::try_from(...) and propagate or panic with expect including
the offending value), e.g. convert pushed and popped to i32 via try_from and
subtract normally, and update StackEffect::effect() to rely on this safe
conversion; also fix the "SAFTEY" typo to "SAFETY" in the comment to avoid
confusion.