[OMEGA-350] Add unit tests for LLM token-budget handling

[TossSky]

Description

Follow-up to #337, based on its branch. Unit tests only, no behaviour change.

Autotests/unit/test_llm_budget.py (15 tests), registered in run_mandatory, covers what #337 added: the finish_reason and incomplete_reason checks before the notice, the notice itself on an empty reply that ran out of budget for OpenRouter, OpenAI and ASI:One, the ASI:One reasoning budget mapping, the OpenRouter reasoning body, [LLM_USAGE] at INFO on both APIs, and an API error returning an empty string. The provider modules are loaded by file path with openai and config stubbed, so the tests need no container, network or token.

Earlier versions of this PR also changed provider behaviour: a retry without reasoning, one notice per streak, and keeping a truncated reply out of the loop. All three are dropped after the discussion here and in #337.

How Has This Been Tested?

CI: tests/pytest.sh 65 passed, Phase 1 144 passed (129 + 15 new), Phase 2 6 passed, MeTTa tests green.

Checklist

• PR contains autogenerated code
• Self-review completed
• Test scenarios above are passed with the version of the code from PR