Extend arc/settings/settings_test.py to cover all external adapters

[alongd]

Follow-up to a review comment by @kfir4444 on #887.

Context

PR #887 adds arc/settings/settings_test.py, the first unit-test module for arc/settings/settings.py. It currently covers only the two adapters that PR introduces:

• Discovery globals exist after import — GOFLOW_PYTHON, GOFLOW_REPO_PATH, GOFLOW_CKPT_PATH, GOFLOW_FEAT_DICT_PATH, RITS_PYTHON, RITS_REPO_PATH, RITS_CKPT_PATH.
• The adapter is not silently enabled by default — test_ts_adapters_does_not_include_goflow_by_default / ..._rits_... assert that a heavyweight adapter stays opt-in via the user's ts_adapters list.
• The default ts_adapters list is exactly what we think it is — a tripwire against shipping an unintended default.

Ask

Extend the same pattern to the other externally-installed adapters that settings.py discovers or exposes: AutoTST, TS-GCN, KinBot, xtb / xtb_gsm, Sella, TorchANI, UMA, and any ESS/TS adapter added later.

For each, assert:

1. Every settings global the adapter depends on is defined on the module after import (catches a rename, or a discovery helper that silently stopped being called).
2. The adapter's presence in / absence from the default ts_adapters list matches intent — heavyweight or gated adapters (UMA is model-gated; GoFlow and RitS pull multi-GB envs) must not be on by default.

The two test_ts_adapters_does_not_include_*_by_default tests in settings_test.py are the template.

Notes

• These are pure import-time assertions — no external env, checkpoint, or network needed, so they run in the standard CI lane.
• Path-discovery logic itself is tested separately in arc/settings/external_paths_test.py; this issue is only about the settings-module surface.
• Out of scope for Add GoFlow and RitS TS search adapters #887 by the reviewer's own request.