[Tests] Add manual picture loader benchmark against the real card hosts (#7288)

* tests: add manual picture loader benchmark against the real card hosts

(cherry picked from commit 588d71d3b9a8278ab98b847802908f322c1035b7)

* tests: address review on picture loader benchmark

- Sandbox via unique app/org names plus Linux-only XDG redirection, derive
  the warm-cache probe and data path from SettingsCache, and bail out when the
  temporary sandbox cannot be created.
- Run each pass with a fresh worker and shut workers down before reading the
  429 counters, so the redirect cache is persisted and no worker thread can
  outlive the stack-local counters or the installed message handler.
- Make s_activeCounters atomic and always forward log output when the previous
  handler is the built-in (nullptr) one.
- Validate --timeout-min, scale the cached-pass budget with --count, honour the
  first --url as the stress template, and add the missing trailing newlines.
- Zero-initialise SettingsCache members so the benchmark mock cannot
  dereference an indeterminate pointer.

---------

Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>

tests/picture_loader_benchmark/CMakeLists.txt

@@ -0,0 +1,26 @@
+# Manual benchmark hitting the real card image hosts. Not registered with
+# add_test(): it requires a cards.xml, touches the network for minutes at a
+# time, and needs network access. Build it explicitly and run by hand.
+add_executable(
+  picture_loader_benchmark_test
+  ${VERSION_STRING_CPP}
+  ../../cockatrice/src/interface/card_picture_loader/card_picture_loader_local.cpp
+  ../../cockatrice/src/interface/card_picture_loader/card_picture_to_load.cpp
+  ../../cockatrice/src/interface/card_picture_loader/card_picture_loader_worker.cpp
+  ../../cockatrice/src/interface/card_picture_loader/card_picture_loader_worker_work.cpp
+  ../../cockatrice/src/client/settings/cache_settings.h
+  picture_loader_benchmark.cpp
+  settings_cache_mock.cpp
+)
+
+target_include_directories(picture_loader_benchmark_test PRIVATE ${CMAKE_SOURCE_DIR}/cockatrice/src)
+
+target_link_libraries(
+  picture_loader_benchmark_test
+  libcockatrice_card
+  libcockatrice_settings
+  libcockatrice_interfaces
+  libcockatrice_utility
+  Threads::Threads
+  ${TEST_QT_MODULES}
+)