Refactor Vizio tests: shared fixtures, snapshot_platform, reduced parametrize

[raman325]

Proposed change

Refactors Vizio integration tests to address review comments from #165820:

• Shared fixtures in conftest: Added mock_tv_config_entry and mock_speaker_config_entry fixtures plus a setup_integration helper, eliminating duplicated MockConfigEntry creation across test_remote.py, test_media_player.py, and test_init.py
• snapshot_platform: Added snapshot-based entity setup tests for both remote and media_player platforms, capturing complete entity state + registry entries instead of manual 2-3 field assertions
• Reduced parametrize lists: Trimmed exhaustive command lists in remote tests to representative subsets (TV valid 5→3, speaker valid 10→3, speaker invalid 4→3) while retaining case-insensitivity coverage

Type of change

• Code quality improvements to existing code or addition of tests

Additional information

• This PR is related to issue: Add remote platform to Vizio integration #165820

Checklist

• I understand the code I am submitting and can explain how it works.
• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
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• The code has been formatted using Ruff (ruff format homeassistant tests)
• Tests have been added to verify that the new code works.
• Any generated code has been carefully reviewed for correctness and compliance with project standards.

To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.

[Copilot]

Pull request overview

This PR refactors the Vizio integration test suite to reduce duplication and improve coverage/readability by centralizing config-entry setup and using snapshot-based entity assertions.

Changes:

• Added shared MockConfigEntry fixtures and a setup_integration helper in tests/components/vizio/conftest.py.
• Introduced snapshot-based entity setup tests for the remote and media_player platforms (with platform-limiting fixtures to satisfy snapshot_platform constraints).
• Simplified/trimmed remote command parametrization while preserving representative and case-insensitivity coverage.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/components/vizio/conftest.py	Adds shared TV/speaker config entry fixtures and a helper to set up the integration consistently.
tests/components/vizio/test_remote.py	Uses shared fixtures/helper; adds snapshot-based setup test and limits loaded platforms to remote for snapshots.
tests/components/vizio/test_media_player.py	Uses shared fixtures/helper; adds snapshot-based setup test and limits loaded platforms to media_player for snapshots.
tests/components/vizio/test_init.py	Refactors setup to use shared helper/fixtures, keeping existing assertions intact.
tests/components/vizio/snapshots/test_remote.ambr	Adds snapshots for remote entity registry entry + state.
tests/components/vizio/snapshots/test_media_player.ambr	Adds snapshots for media_player entity registry entry + state.