fix(testing): name the test binary after project_name (Windows/Linux desktop)

Windows and Linux `flet test` failed after a successful build with
`Unable to start executable ... Failed to find "<project_name>.exe/binary"`.
Root cause (the "doesn't build on desktop" hypothesis was wrong — Flutter does
build): the Windows/Linux runner sets the executable OUTPUT_NAME to
`artifact_name`, but `flutter test -d <desktop>` launches the binary by the
Flutter pubspec `name` (== project_name). When `[tool.flet] artifact` differs
from the project name (e.g. `flet-test-counter` vs `flet_test_counter`), the
built binary and the launched path don't match. macOS is unaffected (its `.app`
is located by the product/artifact name).

In test mode, pin `artifact_name = project_name` so the desktop binary's name
matches what the integration-test host launches. Verified: macOS still passes
(now builds `flet_test_counter.app`); fixes the Windows/Linux launch path.

Author: FeodorFitsner

sdk/python/packages/flet-cli/src/flet_cli/commands/build_base.py

@@ -893,6 +893,13 @@ def setup_template_data(self):
             or self.get_pyproject("project.name")
             or self.python_app_path.name
         )
+        # Under integration test, `flutter test -d <desktop>` launches the built
+        # binary by the project name (the Flutter pubspec `name`), but the
+        # Windows/Linux runner sets the executable's OUTPUT_NAME to artifact_name.
+        # When they differ (e.g. `artifact = "my-app"` vs project `my_app`) the
+        # test host can't find the binary. Pin them equal in test mode.
+        if getattr(self, "test_mode", False):
+            artifact_name = project_name
         product_name = (
             self.options.product_name
             or self.get_pyproject("tool.flet.product")