test: Give each C data integration test its own temp file

[rustyconover]

NanoarrowIntegrationTestSchema and NanoarrowIntegrationTestBatch (c_data_integration_test.cc) write their JSON to the same file, c_data_integration.tmp.json, in the working directory. gtest_discover_tests() registers each gtest case as a separate ctest test, so ctest -j runs the two as parallel processes. One can then overwrite or remove the other's file. When that happens the Batch test reads the Schema test's JSON and fails with:

Expected num_batch between 0 and -1 but got 1

In a full ctest -j 12 run it fails now and then. I hit it on three unrelated branches in one day. With only these two tests running they start together, and on main ctest -R NanoarrowIntegrationTest -j 2 failed 199 of 200 runs. Run serially, both pass.

With this PR, TempFile includes the current test's name (c_data_integration.<test name>.tmp.json), so each test gets its own file. It's still written to the working directory, as before, which the existing comment keeps for portability. After the change the same loop failed 0 of 200 runs, and no temp files are left behind. Full ctest passes (macOS arm64, Debug, 388 tests, three runs).

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.24%. Comparing base (e5f3d0a) to head (54f30ee).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #969   +/-   ##
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  Coverage   78.24%   78.24%           
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  Files         106      106           
  Lines       16901    16901           
  Branches     2012     2012           
=======================================
  Hits        13224    13224           
  Misses       2435     2435           
  Partials     1242     1242           

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