test: add unit tests for `api/`

[KRRT7]

Parent: #2079

Phase 1 — API module

Module	Stmts	Current coverage
api/	487	25%

Key files to cover:

• api/aiservice.py (322 stmts, 25%) — AI service communication, optimization requests
• api/cfapi.py (165 stmts, 25%) — CodeFlash platform API calls

Mock all HTTP calls. Test request construction, response parsing, error handling, and retry logic.

Target

100% coverage for api/ (~487 statements).