feat: New Player::AddRegeneration method

[MS-crew]

Description

Describe the changes
Added a method to apply health regeneration to players via RegenerationProcess, allowing for customizable delay, rate, duration, speed multiplier, and HP multiplier.

What is the current behavior? (You can also link to an open issue here)
No built-in or easily accessible method to apply custom regeneration effects to players through EXILED.

What is the new behavior? (if this is a feature change)
Players can now receive configurable health regeneration via AddRegeneration() extension method.

Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
No breaking changes. New functionality added in a backward-compatible way.

Other information:
Designed as an extension for easier integration with plugins and custom commands.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentations

Submission checklist

• I have checked the project can be compiled
• I have tested my changes and it worked as expected

Patches (if there are any changes related to Harmony patches)

• I have checked no IL patching errors in the console

Other

• Still requires more testing