Optimize & clean up RadiationSystem

[ElectroJr]

About the PR

Over time some PRs have carelessly added some expensive checks to code in radiation system that could be a hot path. This PR removes that, while also just cleaning up parts of radiation system.

Why / Balance

Performance is good

Technical details

• GetAdjustedRadiationIntensity now avoids allocating a list and returns early. Also no more linq.
• GetAdjustedRadiationIntensity is now only called once per source & receiver, instead of once per (source+1)*receiver
• Component fetching and Intensity scaling by stack count is now computed once per source instead of per source*receiver
• OnIrradiatedEvent is now a struct event
• RadiationRay is now a struct, and various debug related collections are no longer allocated unless debugging is enabled.
• RadiationRay now uses EntityUid instead of NetEntity. Debugging uses a separate DebugRadiationRay struct that uses NetEntity.

Media

AFAICT It still seems to work, through I didn't do any thorough testing.

Content.Client_MnqaoYSTyX.mp4

Requirements

• I have read and am following the Pull Request and Changelog Guidelines.
• I have added media to this PR or it does not require an ingame showcase.

Breaking changes

I guess the radiation ray changes are technically breaking, but Its pretty small and I doubt downstreams use the class directly, so probably fine W/O #codebase-changes.