[Mosch0512]

Summary

Running the whole test_item_database_files binary in one process crashed in "A description is in the UI's language also when the item names stay English" (from #813):

test_item_descriptions.cpp(135): FATAL ERROR: test case CRASHED: SIGSEGV - Segmentation violation signal

• Why: once a test has loaded the item data, the item data handler follows every UI language switch and refills ItemAttribute. In the test binary, ItemAttribute is null outside a ClientDataScope, and this test switches the language outside one.
• Why CI didn't see it: CTest runs every test case in a process of its own (doctest_discover_tests). Running the binary as a whole, as an IDE does, crashes every time. Two test cases are enough: "Loading item data fills ItemAttribute in the UI locale", then this one.

The fix:

• The test switches the language inside a ClientDataScope, so it has an item table of its own.
• It turns "Translate item names" off with g_ItemDataHandler.SetTranslateItemNames(false). Before, it only set the item database's display locale to English. Once the item data was loaded, the handler overrode that on the language switch, so the item names weren't English any more and the test no longer tested what its name says. It now checks that the names stay English.
• ClientDataScope's comment says that a test which switches the UI language needs one.

Only tests change.

Related issues

Follow-up to #813 (step 1 of #815).

Checklist

• I have read and followed docs/CODING_RULES.md.
• I have built the project locally (see docs/build/README.md).
  • Windows x64 Debug: test_item_database_files passes as a whole (160 test cases), also in three random orders (--order-by=rand). With main's version of the test, the same build crashes as above.
  • The changed lines pass clang-format 21.1.8.
• Changes are focused on one concern; the diff is as small as it reasonably can be.