Make SimpleExpression more expression conformant

[terrorfisch]

No description provided.

[github-actions]

Test Results

    6 files  ±    0      6 suites  ±0   2m 24s ⏱️ - 2m 26s
  684 tests  -   548    642 ✅  -   534   42 💤  -  14  0 ❌ ±0 
4 070 runs   - 3 288  3 816 ✅  - 3 112  254 💤  - 176  0 ❌ ±0 

Results for commit 7d27495. ± Comparison against base commit 6b23c89.

This pull request removes 548 tests.

tests._program.loop_tests.LoopTests ‑ test_cleanup
tests._program.loop_tests.LoopTests ‑ test_cleanup_single_rep
tests._program.loop_tests.LoopTests ‑ test_cleanup_warnings
tests._program.loop_tests.LoopTests ‑ test_compare_key
tests._program.loop_tests.LoopTests ‑ test_depth
tests._program.loop_tests.LoopTests ‑ test_flatten_and_balance
tests._program.loop_tests.LoopTests ‑ test_flatten_and_balance_comparison_based
tests._program.loop_tests.LoopTests ‑ test_get_measurement_windows
tests._program.loop_tests.LoopTests ‑ test_is_balanced
tests._program.loop_tests.LoopTests ‑ test_is_leaf
…