Test failures on s390x

### Description

Hi,

I've just updated the charmbracelet/x library for Debian, and there are five tests failing on the s390x architecture, see the output below:

```
--- FAIL: TestTerminal (0.03s)
--- FAIL: TestTerminal/DCH_Split_Wide_Character (0.00s)
emulator_test.go:1802: line 1 doesn't match:
want: "A 123 "
got: "A13 "
--- FAIL: TestTerminal/ECH_Multi-cell_Character (0.00s)
emulator_test.go:1802: line 1 doesn't match:
want: "X BC "
got: "XC "
--- FAIL: TestTerminal/EL_Erase_Right_Multi-cell_Character (0.00s)
emulator_test.go:1802: line 1 doesn't match:
want: "AB "
got: "ABD "
--- FAIL: TestTerminal/EL_Erase_Left_Multi-cell_Character (0.00s)
emulator_test.go:1802: line 1 doesn't match:
want: " DE "
got: " E "
--- FAIL: TestTerminal/ED_Erase_Below_with_Multi-Cell_Character (0.00s)
emulator_test.go:1802: line 1 doesn't match:
want: "AB橋C "
got: "ABC "
```

It looks like all failures are related to wide unicode characters. I suspect it might have to do with the big endian architecture of s390x. However, I didn't have time to further dive into this. Maybe you already have an idea what the cause of those failures might be. If you need to test your fix on s390x, please reach out to me, I can run the tests again on that architecture.

Regards,
Tobias

### Version

_No response_

### Environment

_No response_

Start with the failing cases in emulator_test.go around line 1802: DCH, ECH, EL, and ED handling of wide Unicode characters. Run the affected TestTerminal cases on a native or emulated s390x environment and compare their behavior with another architecture. Done means all five reported cases pass on s390x without regressing the existing terminal tests.

Written by the indexing model from the issue text.