Some small Monoprice fixes

[OnFreund]

Proposed change

1. Fix unloading of config entry (by unsubscribing to the update listener).
2. Use suggested value (instead of default) for source names, so they can be easily removed in the options flow.
3. Try to automatically detect zones on first run.
4. Don't call update() before adding to the entity registry on subsequent runs, to speed boot up and avoid warnings.

Also added myself as a codeowner since over the past few weeks I've basically re-written it.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue: Monoprice: zones 21-26 and 31-36 do not show up in Lovelace starting from 0.108 #34035
• Link to documentation pull request: Update Monoprice docs to reflect recent changes home-assistant.io#13262

Checklist

• 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
• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• Untested files have been added to .coveragerc.

The integration reached or maintains the following Integration Quality Scale:

• No score or internal
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• 🥇 Gold
• 🏆 Platinum

[probot-home-assistant]

Hey there @etsinko, mind taking a look at this pull request as its been labeled with a integration (monoprice) you are listed as a codeowner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[MartinHjelmare]

If you split this PR into five PRs reviews will be faster.

[OnFreund]

@MartinHjelmare thanks. I understand and appreciate the logic - but most of these are either really small (1, 2, code owners), or related (3 & 4 go together). Is it worth the extra pipelines, etc? If it is, I'll split it up a bit.

[MartinHjelmare]

It's always worth it to make PRs smaller. Smaller PRs skip the line. Smaller PRs are easier to review so less risk of bugs. Smaller PRs have less things to talk about so the review iteration will be shorter.

[OnFreund]

OK, here's the first small PR in this series: #35107

[OnFreund]

Two more:
#35111
#35112

That last one will be hard to merge before #35112, so I'll wait for that one

[OnFreund]

The final PR:
#35127

[OnFreund]

Since this is all covered by smaller PRs now, and only one of those hasn't been merged yet, I'm closing this, in hope that #35127 gets reviewed and merged soon.