Handle split keyboard watchdog and os detection resets in a unified way.

[hydra]

Description

• reset delegated to the main task.
• user code from pre_mcu_reset_user is executed before a reset.

Additionally, I've taken similar approaches in other firmware that I'm a maintainer or author of, it allows graceful shutdown in a single place.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout (addition or update)
• Documentation

Issues Fixed or Closed by This PR

• None, but was developed due to this: [Bug] interconnect on infinity ergodox broken in latest firmware #19420 (comment)

It allowed me to hook into the reset code and set the backlight color on an ErgodoxInfinity, and also to update the display with the reason prior to the reset. It was invaluable for debugging.

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).