Fix backtrace test on some linux versions

[SirTyson]

Description

Fixes "backtraces work" tests.

It looks like this test is too brittle. On my laptop, I get correct backtraces that are formatted like this:

backtrace:
   0: stellar::printCurrentBacktrace()
             at src/util/Backtrace.cpp:27:22
   1: C_A_T_C_H_T_E_S_T_0
             at src/util/test/BacktraceTests.cpp:15:5
   2: invoke
             at src/../lib/catch.hpp:14169:15
      invokeActiveTestCase
             at src/../lib/catch.hpp:13025:27
      runCurrentTest
             at src/../lib/catch.hpp:12998:17
   3: runTest
             at src/../lib/catch.hpp:12759:13
   4: execute
             at src/../lib/catch.hpp:13352:45
      runInternal
             at src/../lib/catch.hpp:13562:39
   5: run
             at src/../lib/catch.hpp:13518:24
   6: runTest
             at src/test/test.cpp:488:22
   7: operator()
             at /usr/lib/llvm-20/bin/../include/c++/v1/__functional/function.h:436:12
      operator()
             at /usr/lib/llvm-20/bin/../include/c++/v1/__functional/function.h:995:10
      run
             at src/main/CommandLine.cpp:554:12
      handleCommandLine
             at src/main/CommandLine.cpp:2195:25
   8: main
             at src/main/main.cpp:382:15

While the backtrace is working, the test fails, since we look for a very specific string Catch::TestCase::invoke, which may not exist depending on what format you get based on your version matrix. It looks like Catch automatically generates test functions with the name C_A_T_C_H_T_E_S_T, so this string should appear no matter what formatting we get on the backtrace.

Checklist

• Reviewed the contributing document
• Rebased on top of master (no merge commits)
• Ran clang-format v8.0.0 (via make format or the Visual Studio extension)
• Compiles
• Ran all tests
• If change impacts performance, include supporting evidence per the performance document

[Copilot]

Pull request overview

This PR fixes a brittle backtrace test that was failing on some Linux versions due to platform-specific formatting differences in backtrace output. The test was searching for a very specific string Catch::TestCase::invoke which doesn't always appear in backtraces depending on the compiler and system version. The fix replaces this with a more robust check for C_A_T_C_H, which is part of the test function name that Catch2 automatically generates for all test cases.

Changes:

• Replace brittle backtrace string matching with a more platform-independent check
• Add defensive empty check for backtrace output