test: increase unit test coverage (cloud, cover, remote, datetime, config_flow, entity)

[lweikit]

Adds unit tests for existing Python code — no production changes. This is the "complete the remaining unit tests" item from the README's Contributing section.

Coverage across the six modules goes from 43% → 94% (502 lines newly covered):

Module	Before	After
cloud.py	25%	99%
cover.py	34%	98%
remote.py	31%	93%
datetime.py	31%	88%
config_flow.py	53%	91%
entity.py	85%	94%

test_config_flow_extended.py complements the existing test_config_flow.py (cloud/scan/search/connection paths). All 379 suite tests pass; ruff check, ruff format --check and the existing tests are clean.

🤖 Generated with Claude Code

[make-all]

These tests should be merged into test_config_flow.py rather than adding a new file.

[make-all]

These files should be merged to the existing entity test files.

[lweikit]

Thanks for the review. I've merged the new tests into the existing per-module files and removed the parallel files:

• test_cover_unit.py → test_cover.py
• test_datetime_unit.py → test_datetime.py
• test_remote_unit.py → test_remote.py
• test_config_flow_extended.py → test_config_flow.py

Two remain as new files — test_entity.py (base TuyaLocalEntity) and test_cloud.py (the Cloud class) — because those modules had no existing test file to merge into. Happy to relocate them if you'd prefer a different home (e.g. base-entity tests in test_device.py).

Full suite passes (379 tests) and ruff check / ruff check --select I / ruff format --check / yamllint are all clean.