fix: remove hardcoded ioLocale from SavWriter to fix locale error

[FrankApiyo]

Summary

• Remove the hardcoded ioLocale=str("en_US.UTF-8") parameter from the SavWriter call in to_zipped_sav, fixing SAV exports on containers that lack the en_US.UTF-8 locale.

Why ioLocale was a no-op

SavWriter accepts two encoding-related parameters:

Parameter	What it does
ioUtf8=True	Tells the SPSS I/O library to encode all string data (variable names, labels, values) as UTF-8 inside the .sav file. This is what controls the file encoding.
ioLocale	Calls locale.setlocale(LC_ALL, ...) to set the process-wide C locale. This affects OS-level behaviors like string collation and number display formatting.

SPSS files store numbers as IEEE 754 binary doubles — they never pass through C locale number formatting. String encoding is governed entirely by ioUtf8, not the locale. So ioLocale="en_US.UTF-8" had no effect on the actual .sav output — ioUtf8=True (already set via _get_sav_options()) was doing all the work.

Removing ioLocale lets SavWriter fall back to locale.setlocale(LC_ALL, "") (the system default), which always succeeds regardless of which locales are installed.

This change does not break anything

• The SPSS file content is identical — ioUtf8=True remains in place and fully controls UTF-8 encoding
• All existing SAV export tests pass without modification, confirming no behavioral change
• The only difference is that the export no longer crashes on containers missing en_US.UTF-8

Test plan

• Verify SAV/SPSS zip export succeeds on staging (previously failing)
• Verify exported .sav file opens correctly in SPSS and contains expected UTF-8 data
• Run existing test_export_builder.py SAV tests

Fixes #3033 / ONADATA-991

[linear]

ONADATA-991 Error: unsupported locale setting