test: Mobile test runner

[limbonaut]

This PR:

• Introduces a custom test runner, that can be executed directly from code, and bumps gdUnit4 to required commit.
• Updates CI to use the new test runner, since it improves readability in GH logs.
• To initiate tests, the demo project expects the following environment variables to be set:

  SENTRY_TEST=1
  SENTRY_TEST_INCLUDE="res://test/suites/"   # ";"-separated list of files and/or directories

  • Additionally, these variables can be set via Android extent extras using the same names.
• Adds a tool button to run tests straight from the demo project for convenience.
• Adds a script to run tests on Android on a locally connected device.
• Adjusts tests for Android platform specifics, and removes mobile tests, which are no longer needed.
• Depends on chore: Use threads interface on Android for script stack traces #436

#skip-changelog

[cursor]

Bug: Misleading success hides critical command errors.

The abort_on_error call checks the exit code of the array assignment TEST_PATHS+=(...), not the find command itself. Array assignments succeed even when find returns no results, making this error check ineffective. If find fails (e.g., directory doesn't exist), the assignment still succeeds with an empty result, and the error goes undetected until the later check at line 204.