🔒 [security fix] Fix unwrap() panics when converting C strings

[filmil]

🎯 What: The vulnerability fixed is the use of unwrap() when converting C strings to Rust strings in rust_icu_uloc.

⚠️ Risk: If the underlying ICU library returns a string that is not valid UTF-8, the current code would panic and crash the application.

🛡️ Solution:

• In ULoc::get_available, unwrap() is replaced with the ? operator to propagate any UTF-8 conversion errors.
• In ULoc::iso3_language and ULoc::iso3_country, to_str().unwrap() is replaced with to_string_lossy() to avoid panics while maintaining the existing API signature.

These changes ensure the library is more robust against unexpected input from the underlying C library.

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PR created automatically by Jules for task 17310211343422451087 started by @filmil

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