Allow zeroconf instance sharing

[balloob]

Breaking change

Proposed change

Zeroconf instances are expensive. @bdraco noticed that each Homekit instance has their own instance, and on big networks it's eating CPU.

This new approach allows the zeroconf instance to be shared.

For integrations to use it, zeroconf needs to be in either dependencies or after_dependencies so that a user can configure the used interface.

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

Example entry for configuration.yaml:

# Example configuration.yaml

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:

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
• 🥈 Silver
• 🥇 Gold
• 🏆 Platinum

[probot-home-assistant]

Hey there @robbiet480, @Kane610, mind taking a look at this pull request as its been labeled with a integration (zeroconf) you are listed as a codeowner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[bdraco]

Without sharing

python3 24892 root   42u     IPv4           88999451      0t0      UDP *:mdns 
python3 24892 root   43u     IPv4           88999452      0t0      UDP *:mdns 
python3 24892 root   81u     IPv4           89000658      0t0      UDP *:mdns 
python3 24892 root   89u     IPv4           89001374      0t0      UDP *:mdns 
python3 24892 root   90u     IPv4           89000659      0t0      UDP *:mdns 
python3 24892 root   91u     IPv4           89001375      0t0      UDP *:mdns 
python3 24892 root   92u     IPv4           89001376      0t0      UDP *:mdns

With sharing

python3 2411 root   42u     IPv4           89066539       0t0      UDP *:mdns 
python3 2411 root   43u     IPv4           89066540       0t0      UDP *:mdns 

Still need to figure out where the 2nd one is coming from but now there is a path forward once its found.

Very nice!

[bdraco]

Unignored everything, verified zeroconf discovery still hapening.

[bdraco]

Will modify homekit in the morning to leverage this (well later today now).

[balloob]

Cast is the other one probably.